I prefer to buy components I need, but buy enough extras to deal with failures or losses easily. E.g. if I'm buying SMD resistors (of reasonably common value &

I prefer to buy components I need, but buy enough extras to deal with failures or losses easily. E.g. if I'm buying SMD resistors (of reasonably common value & package like 4k7 in 0402) I buy at least 100, even if I only need 10. That way when I inevitably drop one or send one flying by forgetting to turn down the hot air flow I can just grab another. And 100 costs $0.56, 10 costs $0.14, so there's not much point trying to save money. When I run out of a cut tape of 100, I know I've used enough of them and I just buy a reel of 10,000 for $15-20. Lifetime supply, easy tracking. That obviously doesn't apply to the more expensive components.