Not everyone produces precum - I don't. Others, on the other hand, tend to produce more precum than semen. It always struck me as being a strange product, as it is obviously surplus to requirements for the purposes of procreation as it makes no difference to a man's fertility whether he generates precum or not. Incidentally, contrary to popular belief, precum is nothing to do with semen or the seminal glands - it is produced by the Cowpers Gland, and the correct name is Cowpers Secretion.
an it cleans out the urethra so that the real stuff (sperm carried by semen) won't be tainted with uric acid. The amazing thing is, the whole body mechanism seems to know when you are having intercourse or just wanking or 'play fucking.'
I'm one of those guys who produces loads of precum. Prostate stimulation and stimulation of the Cowpers gland(which produces precum) makes for huge amounts of precum for me. I can constantly squeeze out precum, for as long as I remain hard. Great fun with forplay and oral. I would always take it and rub it on my wifes nipples, clit or asshole and lick it off. Tastes sweet.