Personally, I like when the Dungeon Master is active enough that he notices when players are stalling and keeps the story going. I know this topic is about the players but if the players just aren't doing anything there should be no reason to wait on them.
Thank you for all the responses I'm glad that I'm not the only one that has observed this. The image placed for this topic is very funny, whoever did it thank you. Personally I like to get in a post each day sometimes twice a day but if more time than this is passing I tend to post my character's future actions regardless of the others.
Players Waiting On Players Syndrome Reviews RPG & Card Board
One of the things that causes extra waiting time is when one player's character has a unique set of skills that everyone else wish they had for their character such as being able to find and remove traps or detect magic. Players want those checked first (Traps and magic) before they move on and if the character with those skills happens to be managed by a slow poke then it means a lot of waiting time for everyone else.
Sometimes players may feel that its the initiative of a certain player as the main figure in the game at the moment. So to make a move without first knowing the action of the main player will probably be jumping ahead.
In the relatively brief time I've been playing Play By Post, I've found many reasons to wait for other players.
They mostly boil down to having little to contribute until additional input is received. Maybe he has asked a question and the other person hasn't responded, maybe he's quietly anticipating something and won't be doing or saying anything else until given reason. Or maybe he's just been talking a bit too much and I don't want to dominate the exchange even more.
Waiting outside of combat can be tolerated but once combat has begun I think everyone needs to be more timely because we pretty much know that everyone will be waiting on the rolls. I think the Dungeon Master can speed things along by just keeping to a time frame no matter who says or does what.