It seems to vary. The more sexually active I am the more semen gets produced. One can increase the volume by arousing yourself a few times beforehand. It doesn't actually bother me too much how much I produce but I have definitely noticed that many women say they are looking for heavy cummers. I expect it is a visual thing for some women. Several women have said they like to see a man ejaculate.
The men who boast about it are probably responding to the preferences of some women. We can be pathetic when we are trying to please.