In my case I'm finding that mulch is not always a good thing. We have rain and high humidity almost every day and so my container garden is constantly wet. I have been having problems with my seedlings not growing. Damp out is one possibility too but I was looking at the garden when I noticed a lot of activity under the mulch. Picked up the piece of pine bark mulch and the soil was swarming with fungus gnats. I had seen them around too. There was also clear signs of fungus spores. (looked like cotton)
Anywho the mulch kept my soil from drying out after the rain. The pots drain out okay but the heat on the post causes the moisture to rise to the surface where it use to condensate under the mulch and keep larvae and pupae comfy.
I removed the mulch and the soil looks healthier for it. I also managed to attract fungus gnat predator mites and they go after thrips too so all in all a good change.