I mean, my collector has greater than zero amounts of sludge in it, and I usually put 150-200k miles on my vehicles, so every little bit helps.
There have also been controlled experiments where valves were weighed before and after controlled duty cycles, with and without a can, and the valves came out with measurable deposits from the can-less runs.
Obviously millions of vehicles run around without cans and don't instantly clog up, but talk to any mechanic who works on direct injection engines, and they will tell you that problems do arise eventually.