Hi,
BITS has this unique strategy where they have collaboration with industry and they try that their students get to know about the work culture of corporate life.
This thing helps the students in a great way as compared to joining a company straightaway.
Coming to your question the allotment is purely based on your CGPA and the preference list you fill on their website.(PS School Webiste)
Try to know the last year stats from the seniors and be very careful in giving your preference list if you are looking for a PPO. Although after PS allotment you can still file a grievance if you are not happy with the station allotted but probability of PS station being changed is same as of you liking the mess food (Pilani Campus).🤣🤣
This answer is as par what i have seen for BE and ME people.
PS- I have not seen great placement stats as far as MBA is considered , the MBA guys were pretty stressed out during PS allotment , a person who is on the same line(i am not) will be the best person to answer this.