With casting, you complete the reloading cycle. Having ample supplies of everything becomes important. Nothing worse than planning out some massive run on reloading to have it cut short because you've run out of a component. My biggest problem with casting is not having all the molds I want. I'm doing pretty well on powder, primers, cases and have about 120-130 lbs of lead to play with. My mistake is that I have ONE mold; 230 gr .451 fp. Works awesome for my 1911 and pietta SAA. What I "need" is 30 cal molds.
To me, Reloading is the Yin aspect of the shooting sport. It's the calm, patient, relaxation that compliments the Yang aspect of explosive excitement of shooting. There's also that deep feeling of satisfaction with the "I made that" aspect of reloading. We often lie to ourselves claiming it's to reduce the cost of shooting and it'll get to that point after 4000-10,000 rounds as a break even point. The truth is that it just completes the cycle.