If you ( one) takes the opinion that it's your teenagers room and they can treat it as they choose, what do you do when they say they want it decorated and furnished in a particular way?
If you've got the money and you'd be redecorating it anyway, let them choose, it's their space. If it doesn't require decorating (i.e., already been done relatively recently - I don't think it's fair to ask a teenager to live in a room that looks like the land that 1972 forgot) then you could offer them the deal as a choice but neither of you should get arsey if the other one doesn't agree.
To this day I do not understand why my parents had such an objection to my room being messy. I cleaned it every week, changed the sheets, cleaned the surfaces (I used to put the stuff on my bed, hoover, then drop it on the floor again). It was an absolute mess, but it was totally hygienic and it was contained.
It made me hopping mad that they thought they had a perfect right to go in to my private space. Where I kept my journals, my love letters, my magazine articles about sex and just personal possessions that I didn't want on display. If a kid is old enough to want privacy, they're old enough to have it respected. Why on earth does it matter if the parent 'isn't comfortable'? What about the young person's comfort?
And as for throwing someone's possessions out because you don't like how they store it in their own space, who in the fuck do you people think you are? How dare you?
Why do the basics of respect and decency so often not apply when parenting teenagers? I know they can be a pain in the fucking arse, but they're transitioning from child to adult. You're the parent and you're supposed to have made the transition already. You're the adult. Set the example.