For transitions and gaps
The pedal hop is the most versatile technique in trials riding. It is an absolute must. With a good kick in the pedals and good synchronisation of body weight shifting, you can leap over a gap from a static position or show off some classy beam transitions. Very clean to land your rear wheel exactly in place of your front wheel too, or to climb up small stuff. In real trials, you can position yourself on the rear wheel with a static hop, and then launch a pedal hop from there.

9 variations of the pedal hop in bike trials.
slash Jump over a gap from a rear wheel position with a basic pedal kick.
slash If you have room for one pedal turn or half a pedal turn, and if the surface is smooth, you can jump over a longer distance, or climb frontally on small stuff.
slash You can use the pedal kick to climb up sideways, without any run up distance.
slash Now, if your starting point is very small, and you must balance on the rear wheel, you can combine the backhop and pedal hop techniques, to hop sideways, and climb sharp on street stuff or any odd rocks.
slash Pedal hop sideways, over a gap and land either parallel to your initial position, or turning 90° during the pedal kick, land perpendicular to your initial position.
slash Jump over a gap or climb on stuff with a pedal kick, but land on the front wheel.
slash Two pedal hops in a row, to bounce the front wheel directly onto an obstacle, and follow up with a front-to-back wheel transfer.
slash Starting from a static position, with "both wheels on a crest", a pedal kick can bring the rear wheel right in place of the front wheel.

How to practice the pedal hop
It takes a while to control the rear brakes to release the back wheel synchro with the pedal kick, and to block it right for landing sharp...Just practice...At the beginning, try to climb on the edge of a small kerb to feel the move.
Also, you can practice starting with the front wheel on a kerb, balancing your body above the rear wheel before the pedal kick, then moving your body forward as you kick the pedal, and sending the bike far forward just after the kick. (the final position will look like the initial balance step, but the rear wheel in place of the front wheel on the kerb). Once you master the move, try it on sharper edges or funny shapes.

If the surface where the rear wheel stands is too rough for a nice roll, or if the rear wheel is not on a crest, then the pedal hop is not the best option. Because the rear wheel may get stuck by some irregularity (i.e OTB crash with style). Then what you need is to do a static hop, pulling all the bike with you in one impulsion.