Economy

Hm. I used to be a pro at CS: Source. I mastered Scout to unrivaled level in my peak condition, so if I could buy it even with sacrificing defensefor it, I'd never made eco even in pro matches. And my team never complained about it, because I was in top 10 players at my place.

I don't know how things are going in CS: GO because I played it for only 50 hours or so, and dropped this game.

I think, that if you can be very efficient with available weapons you can buy right now and you are sure for doing your job, you don't need eco. But if you are an average player - just save money for easy guns.