computeropponen:
I do the same with logging in and logging out. The reason is like followed:
Most time of the week I'm in work. My business is the IT and I am doing support too. From time to time I have a quick look to brainking, if I have some messages, or special games are going on. Nearly every day there is a lot of stress at work, but for important games like tournament games, games with high level player, I want a quiet time for doing my move, because I made too many mistakes in such games, while moving in work bacause I thought the moves are obvious, but they were big mistakes because the opponent made a trap. And after work I have still time consuming hobbies and playing corr. games at other sites, so it can take a few days, before I have some real quiet time for my important games and I have to set priorities between the games at different pages depending on the time left for each move.
For this reason I play correspondence games more often than live games, because I can stop thinking about a game and continueing the following day, which is not possible at over the board games.
I think that most people logging in and logging out have nearly the same reasons for doing this.