in terms of gain, feel, and saturation. the effect is not small at all. if you have enough gain already don't use it but if you need more boost. basically i had a 1086 and a kh-3 side by side at one point and if i turned the gain all the way up on the 1086 it was muddy and too bassy and it didn't crunch right for me, so i put a sd-1 in front and backed the gain down on the module, the boost tightened the low end and gave it the extra gain and crunch i needed and i only used enough gain on the module to get there. then the kh-3, with the boost on it was too noisey and it thinned the tone out a little so i turned the gain up a little more but not full on the module and turned the boost off and it sounded great. the kh-3 had enough gain on its own and through its eq was tight as well on its own. so for some modules it works great and some it may or may not be needed but with experimenting you'll never know. either way i never got more volume out of the amp boosted or not, i 'd say unboosted the amp has a tiny bit more presence to it but its very slight but if you re not getting a certain feel out of it then try the boost. one things for sure at lower volume setting on any 100 watt amp a boost pedal will get a closer feel to a cranked amp. i know now what i like where when and why and without trying it i'd never figured it out.