If the vapor is thick enough, you can feel it as a fullness in the lungs. Some prefer that fullness to throat hit, the feel of nicotine hitting the back of the throat. Also, I think having some vapor is good feedback that you did get a good drag. Psychologically I think it is part of the simulation of smoking - to blow out the vapor in the way you used to do with smoke.
Also VG has another function in vapor. Nicotine is a skin irritant. Medium to high nic in 100% PG can be pretty irritating. People have gotten sore tongue, mouth, throat and even irritated lungs. Having some VG in the mix usually buffers the irritation enough to get rid of the problem.
That said, I prefer more TH and thinner easy to use juices. TH and vapor are somewhat mutually exclusive. You can have thicker
juice w/ more vapor and less TH or thinner juice w/ more TH and less vapor.
I find in standard stuffing cartos, I get the easiest use and best carto life with 20% or less VG, often 10% or less (and also by avoiding juices that drop sediment)