I think the only reason to use Pine is that it is cheap.
The against for me are:
- hard to burn because of the grain
- smells bad (and has lots of smoke)
- not healthy to burn according to this: http://www.sawdustconnection.com/Pyrography-101-Tutorial-Pyrography-Safety.htm
This already sold me to not use it - I actually have a half done big piece that I am not thinking of completing.
But if you are still not convinced then see how the work looks after some time - the Pine photos attached are a year and a half apart, the cutting board is a year and 4 months apart. Both works have a layer of gloss on top (the same kind of gloss actually).
I have found that a coat or two of spar urethane stops it from fading so badly, though. I use spar on most of my pieces anyway; really does a great job protecting from fade... Though nothing seems to stop the pine from taking on that aged patina. :-/