In my experience with the poly glues it really depends on what you are attempting to achieve that will be the deciding factor when it comes to applying moisture or not.

Poly glues applied without moisture will still cure but not as quickly, they also will not foam up and expand nearly as much so the gap filling properties of the glue are diminished if you don't moisten the area first. OF course there are times when you might not want the glue to foam up on you and fixing foam certainly could fall into this area.

As for the moisture in the air being adequate, well that might hold true for some but bear in mind that if you live in the desert southwest of the US or it's the middle of the winter and sub zero outside, there is very little moisture in the air to begin with.

The quick and dirty of it is that if you have a need for a glue with gap filling properties, wet the joint and get ready with the towels and alcohol to wipe up the ooze. IF you just need to bond something that fits together well forgo the added moisture. Poly takes longer to cure without moisture present so working times can be quite long, often overnight. Adding moisture will change the cure ties dramatically and 45 minutes isn't unusual in my experience, no it isn't rock hard after that length of time but you can't pull the joint apart either.