When I'm getting ready to keg my beer, I cold-crash the primary for a couple days down to ~35, add gelatin, continue cold crashing another day or two, and then transfer to the keg. Clear beer goes in the keg, and all of the trub/flocculated yeast/gelatin is left in the primary. Works great every time. When the keg kicks there is very little mess to clean up at the bottom.
As with most things in homebrewing, there are many methods to achieve the same end result. Find what works best for you.