Every time I see posts about custom brushes that ask for your desired loft I have no idea what I should pick or even what the loft does as far as effects. Could someone educate me on this topic? I bowl lather and use both soaps and creams.
Varies, depending on knot size. For an average sized knot, anywhere between 20-24mm, I find <50mm to be best for face lathering and hard soaps. 50-55 is a decent "all-around performance" range. 55+ is more suited to cream and bowl use. YMMV - but this is how I see it.
Of course, that ignores density and hair type - you can get away with more loft in a tightly-packed two-band knot than with a less dense silvertip knot. Boar complicates it further - for me, I can add about 5mm to a "badger" configuration and it's suitable for the same uses if it's a boar (so 55mm Boar = 50mm Badger, sort of).
But, truth be told, there aren't any "rules". You gotta find out what you like. That's why there's so much variety in brushes.