what does playing against the computer do for your chess?

It's not good practice for many reasons.

You could probably use it for specific exercises though, like testing your calculation in positions where there are things to calculate. Maybe you could do this by playing a full game.

interesting

playing against engines (1400,1600 and 1800 for example) gives false confidence...you beat them constantly and still get beat by your level players

It spares you the slight embarrassment of knowing that there's a guy out there somewhere who's thinking "I just wasted this mother, snork, snork."

Honestly, I enjoy playing against the computer, and I personally find that I get a lot out of doing so. Perhaps because, even at low levels, it still regularly beats me. I find it a good way to try new things and take my time to analyze each position, without having a friend on the other side of the board, waiting on me and bored. I basically treat each position like a tactics lesson, exception I got myself in that predicament. If it's a terrible situation without a good solution, I only have myself to blame, and can go back and look at the move history to see where I went wrong.

        There many benefits playing against the computer,and its always available. Remember though, be  sensible. By that I mean try to play it at a level equal or slightly higher than your own,this will give  a chance to win or draw or at least have a chance to enjoy the game more than playing at a level much higher, or lower than your current ability.

    I should always proof read before I hit the "post" button!

You should be able to edit your post after posting. :-)

i agree with the "slightly higher level" part. lately ive been getting worse, with going to school, cant spend at least 8 fully focused hours a day on chess. ive been just playing the play magnus app and it changed my game to a degree, now im more sound and more positional. my friend from albania said his uncle got to 2300 performance in a tournament from mostly using the play magnus app for training and adapting to how it plays. his rival was magnus age 13. currently my rivals are magnus 11 (very close in skill level, about equal) and magnus 12 (close for part of the game but when im not thorough i lose. against magnus 12 my best chances of winning are 40 minute games going into an approximately equal ending.) but, online and over the board i got slightly worse at least from this training. im more back into form today after doing alot of tactics for 2 days. anyway, i texted 2 masters and 1 said "playng a machine never helps your game, it only helps for openings, the same puzzles are the best, then you master them and go deeper in the openings." another responded "tactics, master games/guess the move and books on strategy". basically i just want to improve and get really close to or become a master by the end of this year and beginning of next year. i saw this of course in recent research in a post on improving, not much to do with engines: Possibly of interest:
"... the NM title is an honor that only one percent of USCF members attain. ..." - IM John Donaldson (2015)
http://www.jeremysilman.com/shop/pc/Reaching-the-Top-77p3905.htm
What It Takes to Become a Chess Master by Andrew Soltis
"... going from good at tactics to great at tactics ... doesn't translate into much greater strength. ... You need a relatively good memory to reach average strength. But a much better memory isn't going to make you a master. ... there's a powerful law of diminishing returns in chess calculation, ... Your rating may have been steadily rising when suddenly it stops. ... One explanation for the wall is that most players got to where they are by learning how to not lose. ... Mastering chess ... requires a new set of skills and traits. ... Many of these attributes are kinds of know-how, such as understanding when to change the pawn structure or what a positionally won game looks like and how to deal with it. Some are habits, like always looking for targets. Others are refined senses, like recognizing a critical middlegame moment or feeling when time is on your side and when it isn't. ..." - GM Andrew Soltis (2012)
https://web.archive.org/web/20140708093409/http://www.chesscafe.com/text/review857.pdf
100 Chess Master Trade Secrets by Andrew Soltis
https://web.archive.org/web/20140708094523/http://www.chesscafe.com/text/review916.pdf
Reaching the Top?! by Peter Kurzdorfer
"... On the one hand, your play needs to be purposeful much of the time; the ability to navigate through many different types of positions needs to be yours; your ability to calculate variations and find candidate moves needs to be present in at least an embryonic stage. On the other hand, it will be heart-warming and perhaps inspiring to realize that you do not need to give up blunders or misconceptions or a poor memory or sloppy calculating habits; that you do not need to know all the latest opening variations, or even know what they are called. You do not have to memorize hundreds of endgame positions or instantly recognize the proper procedure in a variety of pawn structures.
[To play at a master level consistently] is not an easy task, to be sure ..., but it is a possible one. ..." - NM Peter Kurzdorfer (2015)
http://www.thechessmind.net/blog/2015/11/16/book-notice-kurzdorfers-reaching-the-top.html
http://www.jeremysilman.com/shop/pc/Reaching-the-Top-77p3905.htm
"Yes, you can easily become a master. All you need to do is some serious, focused work on your play.
That 'chess is 99% tactics and blah-blah' thing is crap. Chess is several things (opening, endgame, middlegame strategy, positional play, tactics, psychology, time management...) which should be treated properly as a whole. getting just one element of lay and working exclusively on it is of very doubtful value, and at worst it may well turn out being a waste of time." - IM pfren (August 21, 2017)
https://www.chess.com/article/view/can-anyone-be-an-im-or-gm
https://www.chess.com/article/view/don-t-worry-about-your-rating
https://www.chess.com/article/view/am-i-too-old-for-chess
https://www.chess.com/article/view/how-can-older-players-improve