Agression and hate aura are vital to a tank who is in a party, if a tank doesnt use hate then the mob will attack the highest DD'er which usually have the lowest def, so its always a good idea to get hate type skills. As for charm ive found no use for it really, just use it if you want to try get past agro mobs.
Charm is simply a negative hate skill... won't really work to get past aggro mobs, all it does is remove a bit of hate, just like the hate skill adds some hate. In a party however, if you share the mob's hatelist with other members (most likely) using charm might just be enough to get the mob off you and onto another party member or someone else that's sharing that mob's hate list...
...I've made like one useful cast of charm once in a duo where I'd probably had died if it didn't work, but compared to the hundreds of casts where it wasn't enough it seems pretty useless. It's good in theory but in practice, it's mainly way too slow casting and with much to long cooldown to recast...
I always thought that if you used charm it turns an agro mob passive, i might be confused with another skill tho. Ive been in parties with a TH in a cata and he used this skill on the agro mobs and we strolled right past without it giving chase.