FWIW, we often castrate. Unless we want to produce a boar for breeding (and there's not a huge demand for them, especially round here), we'll castrate the lot. If we do want to produce a breeding boar, we'll leave intact any boar piglets that look promising, e.g. good number and alignment of teats, no colour defects, not runty.
We castrate because we can then run weaners of the same age together, whatever their sex. Also, we sell a lot of our pigs as weaners, and castration means we can sell a male and female together. Novice pig-keepers are also generally happier having castrated rather than intact boars, as the latter can certainly be rather boisterous as they get older.
Sometimes we get the vet to do it just because of the need for extra pairs of hands, usually we try to combine some other farm business for the same visit. I have castrated them myself: I found it very easy but then I am a doctor in my "day job"! If you want to castrate yours, ask your vet to show you how, and then get them to watch you do a few to make sure you are doing it right!
HTH