RealGM

Sorry if this has been asked before but I have a question of how can teams waive a player.
For example, let's say a team trades for the NYK Roger Mason who is in the last year of his contract. Since he is in the last year, my understanding is that the team can choose to waive him. Although his contract is still on the books, is the reason that it frees up a roster space?

Any further info on how and why players are waived would be appreciated.

Waiving someone does free up a roster spot, yes, but teams won't trade for guys just to then cut them. Not without some incentive to do so, at least, such as the inclusion of a draft pick or cash or something.