My business partners and I created an alt strictly for business purposes. We all have access to this alt, its contents and $L's. We found it easier then assigning permissions, roles etc. and easier to pay land tiers, employees, etc. The 1st thing written on our alts profile is "I am an Alt and strictly for business purposes." so there isn't anything underlying sneakyness or malicious intent. I just recently created an alt for personal reasons. Some days I just want to explore and be by myself. I find that whenever I am exploring a new sim or checking out an art exhibit (which I like to read descriptions or bio's of the artists) or just having fun discovering new things, I get bombarded with IM's from friends and group notices or TP requests and I'm not one to ignore my friends or customers so I end up having to stop what I'm doing and either go vote for a friend somewhere or hit a MM board that only needs 5 more ppl and so on.
I don't know why I didn't create an alt before now! I actually would dread logging in somedays cuz I had a rough RL work day and just wanted to escape by exploring. The newbie alt gets ignored for the most part, is not bogged down with tons of attachments and over primmed hair or clothing so I have less lag.
I would never use it to grief or hurt anyone ever, and if I post I would never use the alt to speak for me but after 2 years on SL, I do see a purpose of an alt. I almost feel like Im in SL to escape RL (if only for an hour at a time) and with the new alt Im in Thrid Life to escape Second Life...LOL