As per the guide, you want to draw out PC with Towers against FG's like EP. Losing either Dials or HG's can be disastrous as you've seen, although it depends on how many you have left. If you draw a lot of HG's and you're able to keep one going, that's usually enough.
In other words, you only want to sacrifice HG's if you have a surplus of them or Dials, or if it's mid/late-game.