Tactics trainer and light-speed tactics
So you load a new puzzle on tactics trainer, your time limit is 20 seconds, you see mate in three instantly, you go for it without hesitating a moment looking foward to +15 and suddenly tactics trainer says „WRONG!“ Too bad, your solution does not work, there was a bishop hanging in the corner of the board. You type frustrated comment saying what a nonsense it is and go for a new puzzle.
I was thinking a lot recently about how useful are puzzles with such a short time limits for your chess improvement.
Great thing about short time limits is that it forces you to optimize the way you calculate. When I see a tempting check but there are 5-6 possible responses I usually give up on the variation and try something else. I really want to make this “something else” work, spend a lot of time on this. Once I realize that there is really no way it works I return to tempting check only to realize that after 5 responses I win material immediately and the 6th one allows mate in 2. Quick time limits force you to gain time by calculating easy variations till the end deciding once and for all whether it works or not.
However, short time limits have one huge drawback. You see mate in 5 or winning a queen for a minor piece leaving your opponent with zero counterplay? In a real game what you should do is calm down, check twice, thrice whether it works or not and only after you are 100% sure, than you go for it. It does not matter whether you spend 1 second or 10 minutes on that, game is simply over. John Emms in his wonderful Survival guide to competitive chess tells you that in such a situation you should calculate every single legal move your opponent has and make sure your solution works after all possible moves no matter how crazy they look. Short time controls teaches you a really bad thing when it makes you blitz the solution out.
All in all, short time controls for tactics winning +2, +3 of material are a great thing to improve your calculation skills. When there is a mating combination or a possibility of winning huge amount of material, they do not make sense.
How to avoid this problem? Probably a very good way of introducing time element to puzzle solving is giving every problem the same time limit, say 2 minutes + 5 seconds increment for very move you make. It would make solving puzzles more similar to real-game situation.