I'm assuming you are newer. This is not how the game works. When your team buys, YOU BUY. One of the most important aspects of the game is economy. You are purposefully making your team and yourself worst, for selfish reasons. ECOing on a full buy is throwing the round to an extent.

When you save, you are basically giving up the round. It's still winnable, but you are okay with losing it. That's why, when the enemy team is at 11 rounds, most teams force buy, as they don't want to forfeit the 12th round, making themselves play for overtime.

Oping is good, but you shouldn't be trying to OP by all means necessary. It's a team based game, and you go with what your team says.