If u have contributed to the organisation u were with, then by all means go ahead and ask for that letter of testimonial. If u know u aren't on too great terms with your supervisor and if he's got nothing nice to say then don't.

In which case, if ur joining a new organisation and putting ur current boss as ur reference, he may still be contacted by the new company.

If I leave my current office now, I surely will ask for a letter of recommendation . Then again, I thought it was a rather dumb thing for some ex-colleagues of mine to have requested for a letter of recommendation. Both his supervisor and GM refused to write him one, and in the end, it was put through to the MD and well, it wasn't too great a recommendation letter in my opinion