To be honest, the reason I rather not do Heroics or Flashpoints is because I'm worried I'll drag others down.
I do okay with the solo-content, even some of the easier heroics. But as soon as it gets harder I have trouble, mainly because I don't really fully understand the mechanics and I'm lousy at tactics.
I prefer the Healer or DPS role but apart from 'one heals, the other attacks fast' I have no idea what it entails. So, long story short. I'm aware of my shortcomings, realise I'm probably never really going to 'get it' so I don't drag others down because of it.
Do I miss a lot of content this way? Yes. Do I miss a lot of loot and exp? Definitely. Do I also miss a lot of anger directed my way for not understanding something? That also but not everyone yells luckily.