The timing and angle is tricky. You have to fire so the laser about half a second before you hit the jumppad.
When you get it right, you'll fly 2 to 3 times higher than usual. If it can be mastered, it would be very useful on some maps. Below are some examples. I got to the heights shown with the laser and a jumppad only. No other weapon, no hook, no special config, no weak gravity). I've marked the jumppad I used with a red arrow.

Capture City - laserpad on the fire hydrant next to the base. Instead of jumping as high
as the short tower, you fly way above the base tower. Great position to rain down terror,
before stealing the flag.

cbctf1 (I forget what the common name is for this map) - laserpad on the lower level.
Instead of jumping as high as the second level, you fly way above the base level. You
can get this high using the right launchpad from the central platform, but this could be
useful if you are going to your home base and the second level is overrun with enemies.
Mental Space - This map seems like it was made for laserpadding. It is so easy to get
picked off here that avoiding the standard flight paths and having more time and distance
in the air could be a huge advantage. I have 3 examples.

Laserpad on the jumppad on the lower level. Instead of jumping as high as the second
level, you fly way above it. Blast the enemy and then go for the steal.

Laserpad on the launchpad heading toward the center platform. Instead of landing on
the lower center platform, you fly above the upper center platform. Snipe the enemy.
They'll have a hard time reaching you.

This is basically the same as the first mental space image. I laserpadded from the
jumppad on the other side. I liked the first image best to show the height. I included this
one because I thought it was a nice angle.
It is easier to do the same thing with a rocket instead of a laser blast, but you take heavier damage, of course.
other keywords so this post can be found in a search: jump pad, jumpad, laserjump