I make a huge starter and then put it in the fridge. On brewday, I decant the spent wort and allow it to warm up to 48 degrees. I chill the wort to 50-52 degrees and pitch the starter. I find that this gives me the best lagers I've ever made. The very slightly warmer wort gives the yeast starter a bit of a jump.
My reasoning is pretty simple. Just like I don't pitch my ales at 90 degrees, and then allow them to go down to 70 degrees, I don't pitch my yeast into lagers 20 degrees higher, either. I'm afraid that fermentation will start before the temperature drops, so the majority of fermentation would occur at too high a temperature.
If you drop the temperature too fast, you may stall the fermentation. If you drop it too slow, the fermentation will happen at a too-high temperature. It's just easier (to me) to pitch at fermentation temperatures.