Last time we looked SIMS didn't have the granularity to allow staff to book only certain rooms for themselves without giving them other rights that allowed them to do undesirable things to the timetable/rooming. Was a while ago and I really should look into it again - the transfer of the timetable into MRBS is a bit of a fudge.
We also use MRBS for other aspects of school life, such as assigning resources - as it works I'm not overly worried about 'fixing' it but as always if a better solution is out there it's worth a look.