Hi Mykl...

When a plumbing system is designed/engineered properly it is considered to be a self-scouring or self-cleaning system in that the waste water going down the drain and the air from the vent will combine to create a turbulent flow to the waste water and will effectively keep the drains clean and free from clogs.

If a vent is clogged it can lead to a more laminar flow of the waste, i.e. slower draining leaving some of the solid waste behind in the pipes which can eventually lead to clogged pipes and other issues.

A clogged vent or non-vented fixture will not "cause" a backup, but it will certainly lead to a clogged drain down the road. Burping/glugging sounds at a drain are the first sign of a clogged vent or an improperly vented fixture.

Why do you ask?

Mark