With a "small" tank, any extra volume of water is helpful. (( my 40 breeder has a 20 long sump )).
Things might have changed over the last couple of years, but IME, hang on the back skimmers are nearly as good as in sump one.
Think that fuges are a great place for macro algae, which is great filtration, in addition to live rock.
A sump allows one to hide heaters, reactors, etc.
Anemones put out a surprisingly large amount of waste, and can be sensitive to that waste, so a fuge/sump will benefit them -- and you.
Sure, it can be done without a sump/fuge/in sump skimmer, but, IMO, it makes things easier to have them.