The pro is Exposure.
Con is you are giving content away for free.
I see some companies submit a ridiculous amount of long duration videos, or allow affiliates to run a muck, with them registering their own watermarks and that leads to brand confusion. When I say a ridiculous amount 30-50 videos a week if not more to every big tube. It gets to a point where if there is so much content out there, I think it devalues your content over time, and surfers just learn to love it on the tubes.
So like anything else in business, I am sure a certain level of it is OK, but it needs to be monitored / policed.

Don't just give away the farm for free, and if youre submitting it around and not seeing results, then stop.