It will add "Gain" in either position, out front or in the loop. In the loop, it helps restore the loss of gain you get by placing a volume box in the loop. So, by using something like the Spark Boost in the loop, instead of a volume box, you can have more control of what's going on. Some boost pedals don't work well in the FX loop, but the Spark Boost seems to work fairly well.
Ok I'll accept that MM, but really I just enjoy a little good natured, humorous back and forth with folks, (especially with @pedecamp ). Just having a bit of fun! I always try not to take little things too seriously, life is much too short! I'll save my seriousness for things more momentous in my life! I think I'll go play guitar with my boost pedal now!
Here’s what I did. I built a sort of master volume control, a 100k pot and in/out jacks. Put that in the loop with a signal boost after. Set the master volume to a suitable level and use the boost when needed. Works!