I have gone thru and completed re-bagging, boarded and boxed about 90% of my collection. The older stuff mainly. The cheap polybags start to look dingy after a few years, and if not stored in a consistent climate they turn yellow fast. All of my existing ones were different sizes (heights and widths) from a variety of manufacturer's and that annoyed my overly anal self. I just wanted consistency and uniformity;not irregularity in the box. Plus, they just looked funny to me.
I haven't looked back.
My preference is to use the silver/golden age size (775M2) because it will fit anything I'm likely to encounter. Doing that gives me the clean uniformity I like in my short boxes. This stuff ain't cheap.
Combine it with the acid free board (so the book doesn't digest itself in the bag) plus the acid free box (overkill, but it fits the bag and boards stunningly well).
These will be last bags and boards I ever need to buy. No more switching them out ever so often because these wont degrade. Here is a nice little guide to help you decide which size(s) are best for your collection.
I spend so much time hunting for treasure, that it just doesn't make sense not to preserve it when I find it.