I believe it is used to thin the silicone so that once applied, finer detail will show through instead of clumping thick silicone. It also allows the peat to be mixed in and applied at once. I have been experimenting a bit and found it quite handy, and used much less silicone. I used the ratio Grimm mentioned in his peninsula build,
I believe its around 2 parts silicone 1 part toulene 1-1.5 parts peat, don't quote me tho, just trying to remember.
Mike