I'll use music during the brainstorming stage while I'm thinking of the scene and gathering my thoughts together, but in writing I usually prefer silence so I don't stuff up my grammar and such.

In regards to music for a post, I've seen and done it a couple of times but it's something that I'm on the fence about. One of my favourite posts had some soft music that could play in the background to set the mood and scene. It was one of the few times where it didn't feel forced and the song was very mellow, but I've tried it before with other styles of music and noticed that sometimes it comes across more tacky if the wrong song is selected.

That's why when character sheets are selected and people say, "Choose a theme song", are not always the best course of action. How you portray your character and the choice of music can really affect the atmosphere? Even choosing similar songs with slightly different lyrics will be enough to change a character entirely, not to mention the development of a character will also disjoint itself from the song if they change too much.

[b]Edit:[/b]
Got an example but it's a bit Off topic so I'll hider it.
[hider=Theme song example]
So here I have two songs that appear in the Binding of Isaac for the Mom's Heart fight:
[url=https://www.youtube.com/watch?v=Zj9Ck3mNP4o]Binding of Isaac[/url]
[url=https://www.youtube.com/watch?v=8pqknpPM2hU]Binding of Isaac: Rebirth[/url]
Rebirth was a remaster of the original game. Ed McMillan went back to the basics and converted the game from Flash to another engine and thus he changed the composer from Danny B to Ridiculon. The fight was the same-(ish), but just changing composers creates an entirely new feel to a set. 

I'm bringing this up as an example to show how adding music to an RP may not always work because the views that people begin to form in their mind will be different to the other people, so character portrayal may not work when you select your favourite songs in iTunes. Large media is different as the songs/themes are usually written for the characters and everyone is seeing the same thing.
[/hider]