Actually.. No. Triggers aren't the only things. They're converted to Jass in any case when you save, so that doesn't change. The most common thing is models and spells and upgrades etc. with the FT-Only tag. And there are a - rare - few functions in FT (something like 3 of them) that are not available in RoC.
I never said triggers were the only thing. In fact, I said nearly everything with the exception of spells and art can be used. I was simply explaining if you just want to use TFT trigger functions in RoC (without doing a full map conversion) you have to convert them to custom text. I know the map reads everthing in JASS.
Anyways, Im curious what 3 functions don't work. I convert maps extensively, and I have yet to come across any functions that don't work in RoC.