I use it to calculate my equity vs a range to determine if an action is +EV.
The calculation can be pretty cumbersome without Flopzilla
For example: I 3bet AKo and get cold 4bet shoved on from the SB.
It folds around to me and I range him on JJ+, AK.
Plug it into Flopzilla and I have 40% equity vs the range. So I need 3:2 pot odds to justify calling off