There are valid reasons for using the Time Bank to it's fullest effect, one simple reason is that the Player already knows he has the "Nut's" and wants to get as much as possible from the other players involved, Dragging your feet and waiting for it to run down can give the impression that either the player is drawing to a hand and is undecisive about it, or just has no Idea what he is doing.
Whatever reason they do have, it is a tactic they have available, and if it works good luck to them, Personally I don't normally do it but I have done on occasion. Some sites give you the option of playing Normal Speed, Turbo Speed or even ultra Turbo that cuts down the thinking time as well as the blind structure, It really is just part of the game and I can tell you from experience some players take a hell of a lot longer to make up their minds in a Live game, I have had to call the "Clock" on some players in a Live event, when they seem to be taking too much time in making a decision.
This option is not available playing On-line but we all understand that there is a time bank for such instances where players are not willing to play faster, and when all is said and done "Patience" is a big part in playing Poker!