I run bare bottom for most of 30+ years. I run what I call bare bottom 2.0, meaning I use some large rubble on the bottom and cover glass & bottom with encrusting corals & Fleshy LPS - monti's, favia's, stylocionellia's, cyanaria's, brains, acantho's, etc
Con's of bare bottom
-- Some fish & animals need sand to thrive e.g. Nassarius snails, wrasses
-- Looks very artificial while empty at first
Con's of sand/gravel
-- Hard to see detritus to vacuum up
-- Flow limited by sand/gravel being blown into water column
-- Can trap excess nutrients and lead to problematic algae
-- Many corals may be smothered and/or cut by sand/gravel