For me - always on the inside when possible. Always wet install. I install a lot of this film.
I push the sale this direction every time if possible.
- helps retain the visual feel of the glass
- makes it last longer
- allows you to install in almost any conditions
The effect is meant to mimic "etching" or sandblasting glass. Not to make it look like you have a big silver sticker on a window.
The only time I have ever done it is if the client is insistent on exterior, or there's already something too heavy or built in front of the glass.