Pros:
Bullet availability, I am never without projectiles, even when the market goes crazy like after Sandy Hook when I started casting
Custom alloys, lubes, sizes, and molds. Casting puts you in control of another set of variables in the accuracy and consistency equation.
Cost, I have never rendered a single wheel weight or lead scrap in my casting career. Its a dirty process, and a great way to expose yourself to some unknown and potentially nasty chemistry I wish to avoid. I pay around $1.50 a pound to wheel weight ingots delivered to my door, ready to go in the casting pot. Even paying for lead, cast bullets are CHEAP, I have traded off my .22's preferring to shoot 38's in their stead. I plink through about 4k 38's a year between my revolver and ruger 77, it provides better practice, and is lot more fun to shoot than 22's ever were.
Cons:
Time, casting good bullets in any real quantity takes time and is a bit of an art form with a very real learning curve. I do a lot of casting in the winter months when I'm not so busy, so it works, but I do spend a bunch of weekend time casting when I could be doing something else.
Cost, good molds are damned expensive, good casting pots can hit the wallet as well. Casting can be done on the cheap, but any moves out of Lee equipment are going to hit the bank account in a noticeable way.