I started reef keeping back when i was 13 in 1996. Back then i kept a small healthy tank, siphoned the sand and was very successful. In the next tank builds, i had read in some of the books and websites that a large clean up crew was necessary. I stuck ardently to the professionals opinions and continued to buy more snails and hermits as they died.
Funny thing was they never solved my problems. Sure i would have a bit of my glass cleaned, but i still had to scrape it. Sure they ate a bit of algae but they didn't lower my nitrates or phosphates. They actually had the opposite effect.
Right now i am going back to how I did it back than in 1996, with NO clean up crew. I have a 400g system and not having any snails, hermits, or shrimp does not bother me one bit. It actually in my opinion eliminates a variable in the ecosystem. I did try some cheap bay shrimp right after cycle but they hated the temp, 80 was too high.
My simple thought is, 'If a snail eats algae or detritus, then poos a few hours later, have i really solved anything?'
Sure some of unwanted nutrients will be consumed and removed from the system, IME i have found these darn things die too often to be worth the money, hassle, or perceived benefits.