There are 3 types of backlash, and 4 types of brakes.
The first is spool start-up overshoot. Centrifugal brakes deal with this the best.
The second is wind backlash, which occurs in the middle of your cast as your lure is approaching its highest vertical point, and gravity is slowing it - mag brakes work best here - the same for wind and light lures.
The last backlash is over-run after your lure hits the water - thumbs take care of this.
The fourth brake type is spool tension, which is a constant load on the spool. While spool tension can brake all 3 types of backlash, it costs the most cast distance.
Thanks Bulldog, this is very useful info for a new baitcaster, not sure I've seen it explained like that before.