Cheaper? That's a "depends" question. No way you can reload cheaper than you can buy military surplus ammo, but hella cheaper than name-brand defensive or match ammo.
Many people who reload do so because they can turn out a more consistent product than a commercial loader, and thus get better accuracy. Plus, you can experiment with combination of bullets, powders, and power to get a load that, for your rifle, reaches its full potential.
Also, if you shoot older calibers, reloading may be the only way to get ammo. Many of the cowboy shooters reload because they don't have a choice.
That's the boat I'm in, actually. I don't like reloading. I resent the time it takes. I would MUCH rather just hand money over for decent ammo. But, for nearly 2 years now, I have not been able to find what I want. I've b*tched about that elsewhere on the forum, I think. So, with the help of a friend who has the tools, I will now be making my own .357 ammo. I'm seriously not happy about it, but there doesn't seem to be another choice.
Brass life varies depending on the quality of the brass to start with and the abuse it takes. Straight-walled brass lives longer than necked-down brass. The more fire you put inside it, the fewer times it will survive. Just remember to inspect it each time! Split cases can be mighty difficult to extract.