Don't just farm when your teammate is dying!
Okay, CS is important, but you might be losing a lot more than a few creeps if you fail to participate in a fight.
At my ELO (Silver 1), I see this mostly on Junglers. Rather than launching a counter gank immediately, they would clear whatever camps they were doing before moving to join the fight. By then, the teammate is either already dead, or it is too late to turn it around.
Honestly, the camp isn't going to go anywhere. The enemy team is going to gain a lot more gold from a kill or objective than you ever will from a camp.
Of course, laners do this as well. Specifically, I see this behavior often on ADCs, especially if the ADC is Vayne. In one of my recent normal games, my ADC Vayne would literally flame teammates for fighting when "I'm in a middle of a wave," and refuse to leave bot lane while there are still farm left behind.
Just don't waste time farming. You are not going to throw the game by missing out on less than 100 gold. However, if you are down one member, you risk the potential to lose a lot more in a 4 v 5.