I think the answers to this question nearly always skip over what I feel is the main point: After primary fermentation is done, beer needs to condition for a short period before it will taste its best.
You can either do that by letting it sit in the primary fermenter, or you can keg it right away and let it sit in the keg. It doesn't have to be kept warm, either. Just put it in your serving appliance, hook up the gas to carbonate it, and let it sit for the same amount of time. Don't hook up the tap line!
There is a minimum period of time required for the so-called "clean-up" period where warm temps and yeast contact help. But I just consider that part of primary, and it's 1 or 2 days, not weeks.
My personal experience is that nearly all of my beers (4-6% ABV) turn a discernible quality corner after 2 weeks conditioning in the keg. At 3 weeks, they are at their peak. And they are carbed and cold and ready to drink!