A lot of it, in my opinion, is snake oil. I have a lot of original screenprints and original film posters, some of which are framed - I pay what I pay for framing (not silly money, but you do get what you pay for) getting them done at a local gallery/framing shop who know what they're about - but I just have a simple stained wooden frame style, and the standard glass, with a float. That seems to have worked out just fine over many years.
If you're buying prints/posters and storing them, rolled is ok - but really, preferably, find somewhere to store them flat.
If you know you're going to pretty much right away go and have piece framed tho, I wouldn't bother taking it out the tube - leave it rolled and take it like to your framers. Equally, if they have been stored rolled a while and then you decide to have one framed, don't roll them back the other way in an attempt to "even them out" or anything like that.
You might want to check with your framers how they mount prints or posters - mostly they are floated in the frame, but ask and they'll tell you what they do (or what the options are). Some people have posters linen-backed for example - but this is usually for damaged posters, and of course involves something being permanently glued to the piece. With a print on decent stock or a poster in good condition I'd suggest it's entirely unnecessary, myself.
With anything with posters or print framing & hanging, especially to begin with - it's
your print and they are the framers. If you're unsure of anything or just want to know no matter how trivial it seems, ask them. They're the experts, not the internets
