If you go OCC, expect to go right to TBS unless you work some under the table deal with your OSO. If you don't start training right away expect to be in Mike Company doing some sort of busy work or working in another company's training office. Maybe you'll get to do IFS or the Martial Arts Instructor course. Also, don't think that PTAD with your OSO thing is something you will do often. That's something PFCs and LCpls do so they can get a break from work and go home. Not something held in high regard for officers to do. It was so great at TBS to hear our XO make fun of people who wanted to go PTAD to work for their OSO. Anyway, with OCC, once you get commissioned, you are a Marine officer and rate benefits as such. You get paid, you get insurance, blah blah blah.
PLC is a different story. Don't ask why, I don't know all the policies and laws behind it, but it works the same for NROTC mids. Yes, once you get commissioned you are a Marine officer. However, until you report to TBS you don't get jack. No pay, nothing. I have a friend who has been doing construction work every day for enough money to survive since he got commissioned in May. Won't start TBS until November. It sucks, I don't know all the reasons why it's done that way, but it is.
Now, if you have first hand experience (i.e. YOU have been commissioned and been through OCS and TBS....NOT 'well I know a guy' or 'my OSO told me' etc etc) with any of this and I messed up part of this, let me know.