When we explain account sharing to people, it's not uncommon that they ask why would I want to share an account?
Usually this objection is grounded in the fact that most people use the same username and password everywhere today, and by sharing, they'd be giving access to all their accounts. We're hoping you'll start changing your habits with LastPass -- let the program do the hard work of remembering usernames and passwords so that you can feel free to pick good passwords everywhere you have an account (using the LastPass Password Generator to do it).
There's lots of reasons you'd want to share an account with someone else -- if you share a bank account with your spouse, isn't it better that you both can use your 'LastPass' password rather than be forced to keep the same password? If you have a special login for work, isn't receiving that password in LastPass a lot easier than having someone email it to you, where you'll have to go searching through your email at a later date?
All of this is predicated on your use of unique passwords for each account, so if there's a reason you're not doing that, we'd love to know.