When you spray the intercooler with a chemical that can evaporate and remove heat quickly, it helps you gain a cooler, more dense, charge of air.

If you wish to test it, put your car on a dyno and make 2 pulls. Now, spray your intercooler with denatured alcohol and make another pull. You will see an increase in measured power. On a mostly stock FD RX7, we saw a gain of 13rwhp.

Water, N2O, CO2, and alcohol all can remove heat.
Is it worth the cost? That's up to you. If your intercooler is small and is getting hot, and you do not have enough room for a bigger intercooler, it probably is. If your IC is not getting warm, it probably isn't.