A friend of mine who browses Reddit uses the app and complained for a loooong time about their phones battery. I always thought it was just their battery shitting the bed, as they do, until they got a new phone and I realized how much battery the official Reddit app actually uses compared to the third party apps. If nothing else, that's a big reason not to use it.
You know now that you frickin mention it, I feel like my battery life has gotten tons better as well since uninstalling the official app a couple weeks ago.