Frenzy charge adivce and tips

I recently crafted some gloves that became pretty good I would like to think.
The Vaal gave my gloves a mod that adds +1 frenzy charges.
This should be super useful I though so I expermimented with getting 4 frenzy charges but that doesn't actually do anything.
What build / weapon / actually uses frenzy charges?
I don't have the trade tab so I can't sell them.