If you know that the plugin is "reducing" the volume, there is
no worry, as you will be removing it for "Mixdown". The purpose
of the plugin is to give you "reference" quality for the mix, but
that is based on the headphones you are using, and the plugin will be removed
from the Master Bus when you mix down and all volumes will be
as they should be. And, as was mentioned, if you watch your levels,
you can disable the "clipping" option when mixing.
Yes, what here is "reference" and you find that your mixes, when moved from
source to source, will remain consistent, and that is what you want.
You can have a GREAT sounding mix in YOUR headphones, but, when it's moved
to another source for playing it will NOT sound the same at all.