One of the things you should really be aware about role play is that it can be quite time consuming. In better sims there is always something going on, you can try hard to achieve perfection in it, you can study a lot, talk a lot and so on. This can lend to the fact that some people are just going to be in the RP sims only for most of their time, neglecting their friends and being there for months.
Then, when the RP phase is over, they need to really start again, since they neglected so many old friends and quite some of them may have removed them from their friends list. So, take the advise, while RP is fun and allright, don't let it become your number one priority, if you haven't started in such a sim directly. You might hurt some people in the process, badly.