Before this forum converted to vBulletin software, it used "categories." The only way to visit the forum was with all posts showing, i.e. similar to the current "Unified View." Assigning individual threads to categories simply made searching the (then much smaller) archive easier, since one was able to bring up each category separately and either scroll through or use CTRL+F on the browser page to locate titles of interest.

I've never found the vBulletin nomenclature particularly good. This is the Large Format Photography Forum. Singular. What vBulletin refers to as "Forums" are in reality the categories of old. I still visit by using a "posts from the last 30 days" search

so that I'm presented with exactly the same all-categories result as was displayed before vBulletin. The dedicated search function is fairly useless, so these days I simply do an advanced search using Google by entering terms of interest followed by

which limits the search engine to what's cached from this site.

Bottom line: "ULF sub-forum," like all the other "sub-forums," is a relatively meaningless term. They're all just tags for threads in the top-level "real" forum. My advice: bookmark the 30-day link I posted above, scan what's new when you visit and read threads of interest. That way you'll get to know everyone here, not need to constantly go back and forth between a bunch of categories and won't miss anything. It's a lot less cluttered too since FS/WTB bumping was limited to once per week.