So my basement, home of my Man Cave, slopes down towards the sump pump well. That saved my amp, subs and speakers when we had a flood in 2007! Don't level your floor unless you are certain that this isn't an issue.
I don't really level much except the speakers, which have adjustable spikes on Sound Anchor stands, and my Thorens TD166MkII. I had custom feet installed to replace the stock feet. These have a leveling adjustment range of about 2", and have racket balls on the bottom in inverted cups. I must replace the balls whenever the old ones lose their elasticity. But according to several bubble levels, the 'table is completely level.