Ok, so knowing the pros and cons, I have experimented with a couple of batches being tossed right on the prior's yeast cake to see how it turns out for me.
I did a Centennial Blonde a bit ago, and the thing TOOK OFF and finished quick, no harm no foul.
So yesterday I threw a bigger (1.080) batch of my IPA onto a yeast cake from a previous batch.
This morning, my blowoff tube (6' long) was full of yeast, as was the container for my blowoff, and the entire bottom of my fermenter fridge, AND a nice long trail across the floor in the room with the fridge.
Doh! What a freakin' mess. Should be fun when I get home from work tonight.