Most preset rigs on every board have a volume pedal attached to them. It's easy to see why- upon trying a board for the first time and getting a feel for the layout, nothing is a simpler demonstration of possibility for a switch or pedal than volume. As a result, a volume pedal is a popular effect to include in many users first rigs. While we'll touch on a few tricks in rig building in another article, the principle between the two will be the same- the Headrush units do run your signal through the effects the way they are laid out in the rig.
For the volume pedal, this means that there is a significant difference to what is put at the beginning of a rig vs the end of a rig-
When you use a pedal at the beginning of a rig, the pedal itself becomes a choke point before the signal gets run through effects and amps. With less signal going through them, it can become a process where the tone is manipulated, similar to changing the volume pot on your guitar. It's even possible to get a clean signal through your normally overdriven or distorted rig by doing so.
When you use a pedal at the end of a rig, the pedal is instead affecting the actual volume of the finished signal path. This is important because if you want it to be a true signal volume for the board, placing it here will do so without affecting the tone; for example, at 50% it would not clean up the sound, but instead give you the same tone with 50% of the volume.
At the end of the day, a volume pedal is not the only way to affect volume- using scenes to turn off/on effects is an effective way to also change volumes for solos without needing to rock the board. Another trick is to assign volume from different effects into the expression pedal- your amp sim volume, the distortion pedal volume, and in that way, you eliminate the need to put a volume pedal at the front of the rig because the volume on the amp or effect is doing so for you.
This is done from the Hardware Assign screen, on the right-hand side where you can change the effect that is being changed by the expression pedal. If you have an effect loaded on the side, simply tapping on the effect in this right-hand column will bring up the effects for you to select which effect in your rig and which parameter you want to edit, seen below as Volume.