Its good practice to cool it down to the temp of your beer. Sure, some people don't care and siphon their beer onto boiling hot priming solution, but that's not ideal. Ideally, you should disturb the beer as little as possible after it has fermented and conditioned, and that includes thermal shock. Will your beer still carbonate, sure, but are you using proper technique, no. Either way, do what you want, just my 2 cents.