Priming plywood for better adhesion of flooring tiles
If you use a proper underlayment (which OSB isn't), you don't usually need to prime when using a roll-on or brush-on adhesive. It is a good idea, however, when using self-stick tiles, which have a less aggressive adhesive. 

When in doubt, read the instructions. If a primer would be beneficial manufacturers aren't shy about saying so. They want your project to succeed as much as you do for liability and reputation reasons.