I will speak for myself , sometimes I multitable so I need some extra seconds in order to take the decision , other times when the spot is marginal I look at my HUD.
Some other times I instantly check when I am out of position in order to misinform my opponent, I do it or with total air or with a strong hand. Finally when I want to bet for value or fire a
bluff I take my time simply because I want to make my opponent rethink his action.Don't forget that for many online players the time to act is the only read, except of course for the size of the bets.
The bad habit I must stop is to snap call some river bets because I think I have them beat. Some tighter folds are needed by me!