There is no such thing as using time 'effectively' when the position is hopelessly lost--there is only time wasting.
Also, reducing the time per move is not always an option due to personal schedules and/or uncontrollable tournament rules.
There's a difference between "hopelessly lost" and checkmate (or stalemate or 50 move rule or three fold repetition or winning on time before your opponent can checkmate you).
No player is obligated by the rules of chess to resign, ever. Now I will agree there are some situations where it may be courteous to resign, however-that is at the discretion of the player who believes his position is hopeless. IF that player believes he has chances to avoid losing, he has every right to play it out.
Let me remind you also there's nothing illegal about players using their reflection time as they see fit (read the rules). In difficult positions it's normal for players to slow down and think harder. Ideally you want to manage your clock so you don't get into difficult positions but stuff happens.
If you believe you're on the winning end of one of these games, and the player starts to slow down - oh, well. You agreed to the time control, and you can't change that time control mid-game (read the rules).
I don't doubt some of those players who slow down are being jerks but you have to remember two things: 1. when the players clock runs out, you win and 2. why not blow off some steam and do some analysis while your opponents clock is ticking?
I still maintain the vast majority of people who post griping about the non-resigners are frustrated because they don't know how to get the job done.
If you're winning, win! Quit whining!
One thing, that seems to help, when feeling the need to slow down, is posting a comment along the lines of "Need some time to think about this" so as to let the opponent Both, know why the slow down is happening, AND to help build their feelings of superiority *hopefully leading to their downfall*
Poison .. A Classic that's NEVER truly out of style