I have reloaded thousands & thousand of rounds in everything from .17 Remington to .458 over the years (plus untold numbers of shotshells). It is nice to be able to brew up a load for reduced recoil or accuracy. Once you buy the equipment and the supplies to do it, you will need to punch out a lot of rounds to make up the cost. The money you save is a tangible thing, but you need to take into account your time as well.
Like shaman said it is almost as easy to knock out 50 rounds as it is to do 20. Twenty is not worth the time to make the effort to me (depending on caliber). I would usually do 100 minimum at a time and sometimes when reloading buddies would get together with multiple presses, we would work for most of the day and turn out a few thousand rounds & go shoot a bunch of them the next day or weekend. You get in the production groove and become like an assembly line. Face it, once you take the time to set the dies up properly and you have the powder measure throwing correct charges of powder, you may as well knock out a bunch. I would weigh every charge early on until I knew the powder measure was staying accurate, then I'd weigh every third or so.
I used to reload .223s by the thousand and burn most of 'em up the next day at the range. No telling how many .38, .357, .41 Mag., .44, & .45's I've cranked out, but I'll bet we kept the people at DuPont busy making more powder. I recently ran out of a lot of 500 rounds I made up for my .308 that lasted 8 years. I switched to factory loads and only had to move the scope a few clicks. When I sold a few guns and cut back on the volume of shooting I was doing, I gave most of my reloading gear to one of my friends. I just didn't have the time or motivation to mess with it much.
I just don't shoot my main deer rifle that much any more and modern factory loads shoot great out of my favorite rifles. There are also a number of different velocity factory loads made to match most shooter's preferences & hunting situations. If you wanted benchrest match-type accuracy then you might think about rolling your own. I probably shoot less than 40-50 rounds a year out of each of my four cartridge rifles and it is not necessary for me to go through the effort to worry about trying to tighten those groups up, because they're fine for hunting...especially because I seldom have the opportunity to shoot over 100 yards in a hunting situation. I can practice out beyond 300 yards at the range, so I know where each gun is shooting.
One major advantage of reloading is if you shoot a caliber that is rare, not as popular, or has been discontinued and factory ammo is hard to find or expensive, it can save you a bundle. You can also tame down recoil to make a bigger gun shoot like a BB gun. A buddy of mine used to hunt with a .30-40 Krag in wet weather and he cooked up some loads that were superior to any you could buy. Wildcat cartridges are the same way. The Weatherby calibers can be reloaded for a lot less money than the factory rounds are sold for.
If you have the time, money, interest, you shoot a lot, or just want to make up your own loads, reloading can be a blast (pun intended). You can also hook up with someone who reloads and often they will work with you about using their equipment if you pay for the supplies (I had a friend who used to do this with me and he'd just buy me extra bullets, powder, & primers for my trouble & use of my gear). I have gotten to the point in my life that I buy factory loads by the hundred and as long as they're the same production lot (check the the box for matching lot numbers) they will shoot well enough for me to hunt with at any ranges I get around here. But that's just me.
Luck Counts, good or bad