I have 2 accounts, one for myself and I pay for my nephew. There is only one PC that runs MS Windows for the both of us and it's at my home. He flies when he visits from school on weekends or holidays as he only has a MacBook at school. I got him his own account so I wouldn't have to account for anything he does in game. I'm sure he'd do nothing to embarrass me but I don't want to have to keep up on any interactions he has with folks. It'd be a PITA at best and disingenuous at worst being a different person behind the in-game handle.
I have had a bad experience sharing an account in the past when I went to the AW convention in 1998. I left my PC and AW account open for anyone to use that didn't bring a PC to Con while I was away touring the aircraft carrier in SF Bay on day 2. Apparently someone(s) used my account to taunt, say vile crap and be complete holes affixed to a derriere in the arena while I was away. It took me a long time to clean that up-especially with one player and friend. Lesson learned.
If it is a problem or seems a problem to the community, I'll certainly shut his account down despite knowing nothing untoward is going on as we can't log on at the same time anyhow. It's not worth anyone even thinking we are sketchy in this regard.