I agree that for PbP, it will help speed things along if we go ahead and roll if we feel it makes sense to, and I also agree that since US is so narrative-driven and making rolls are so up to interpretation, it is totally fair for the MC to say that the roll was unnecessary or disregard it for some other reason.
In my most recent post, I considered asking if I needed to make a roll, but I knew that could possibly slow things up and for telling a lie, the rules seemed pretty clear. I opted to explain what I was rolling and why, though, just so it was really clear on the post. I'll probably keep doing it like that, if I feel like I need to make a roll.