Global setting to disable gem usage
At least three times I've accidentally used gems. It's also happened to all three of my kids. In each case, it's happened when trying to train troops without enough elixir. The "let's use our gems to get more elixir so you can train these ever-so-deserving troops!" window pops up, and the instinct is to hit the button. Wham. Too late, too bad, gems gone. Very frustrating. The lost gem count for us is over 300.
Please consider having a global option that disables all gem usage as an option. This would help the gem savers out there.
My cynical side is thinking that this will not be considered, because gems are a money maker for Supercell. I bet every gem has a dollar amount associated with it, and Supercell will be loath to do this, because it will result in a lower revenue stream. However, the other side of me hopes that Supercell will try to improve the customer experience and reduce this frustration.