There are plenty of threads here detailing advice on increasing semen volume - from commercial products, supplements, general hydration and eating certain foods. Thought I'd share my practical experience.
The zinc/l-argenine definetely does work.I bought mass-market supplements from a multi-national health food chain, and took them in the stated doses. The problem is that it is very difficult to perform a scientific experiment. Hydration levels and abstinence levels vary all the time - but I would say that there is a noticeable increase in the amount of semen produced after a few days of taking zinc / l-argenine. The problem is that it is very difficult to quantify it. I didn't go so far as to cum into teaspoons, and the majority of the ejaculations went inside never to be seen again. But those that I did witness were larger - how much is another issue. Commercial products like Semenax claim up to 700%, which I find difficult to believe in isolation. I would say that the zinc / l-argenine gave a 50-100% increase on the first ejaculation only. Given at least 5 hours in between, ejaculations were about 50-100% increased on what I would have expected normally.
The downsides - well I stopped taking the supplements after a month. The increased quantity certainly made me feel good about myself, and it was the first time I'd ever managed to take supplements of any kind consistently. However, after a fortnight, I suffered considerable stomach aches and diarreah, which have not gone away. After another week, I started to experience joint pain in various small joints - fingers, feet etc. This is a continuous pain, and although I can't with any medical certainty put it down to the zinc - I'm willing to bet that I'll recover in fairly short order after giving up. Walking on one of my feet was painful for a couple of days, and currently my fingers have a dull pain in the ligaments during writing or typing.
It's nice to be able to have large loads - but I can tell you first hand- it isn't worth the downside. I can't recommend it.
On a seperate issue, I did try a two-week total abstinence (without zinc), and the volume produced was far greater than the zinc-assisted.
Not something I've ever been interested in, but it certainly made an interesting read. And after reading your post, I would be naturally wary if my OH suggested trying to chemically enhance the amout of his ejaculate.
I went on zinc supplements a year or two back when we decided to try for a baby, as zinc is said to help with sperm production. I can't say I noticed any change in semen volume at the time, but then I was having sex far more frequently than normal, and as the purpose of the excersise was to ejacualate inside, I can't say I had much option to check.
As for why a guy would want increase semen volume, the reasons that I can think of are:
1) Stronger orgasms are often related to bigger loads. The more semen is ejaculated, the longer the contractions go on for, and the more pleasure.
2) Self confidence. In the same way that guys get obsessed about penis size, I guess we also worry that we compare well with what is produced. It probably doesn't help that in a lot of porn you often see the male star shooting what seems like half a pint across the face of some plastic boobed lady.
As for joint aches, I can't say I suffered from any myself. Maybe to do with the l-argenine, or too high a doseage?
I think asparagus is ment to be one of those super foods, you know the ones that resurect the dead or somthing. but im pretty sure asparagus is very high in iron which helps with the blood, i could see how that effects things.