Time-wasters are primarily new players and, to a lesser extent, dishonorable stronger players including SDKs. I threw in trolls to cover all the bases, but since they are a small percentage of players, they play a small role in this subject as well. Stalling is very common, and stalling to the bitter end is much more common than you imagine.
Stonger players. say mid-DDKs and up, who understand that they do not need to capture dead groups, are able to minimize the lost time, but weaker players are frequently drawn into an endless whack-a-mole routine. Some TPKs, as well as trolls, will also infill their territory, even until they have only one liberty. The trolls, and the normal players who are angry, will drag out each move, by using, say, 25 of 30 seconds for each self-atari move. Stronger players will often resign or escape in order to avoid having their time wasted.
I have seen all of this because I devote a large part of my moderation time to watching games on the Overview page. This enables me to intervene immediately in cases of score cheating and stalling.