I often come across videos showing how the poster describes how he/she attaches conduit and hoses to various tools and use a shop vac as the dc. Never have I seen them insert a second hose to the exhaust and running it to the outside.
I cannot understand why they do not vent to the outside when all that is needed is a second hose for the shopvac, a very inexpensive piece.
What am I missing?

(No, I am not planning to use a shopvac for dc.. Just curious)