You would want to log out for several reasons ...
1. If other people use the same computer
2. If you are using Pet Talk in public place
3. If a friend wants to start a Pet Talk ID of his or her own, with your help!

Logging out when you leave is the safe thing to do if it's not exclusively YOUR computer! And even if it is ... what if theaves broke in in the night, stole your computer, then happened to go to Pet Talk, they could post as YOU! Eeek!

Or your pets could use it while you are sleeping, and post tattle-tale messages about you!