I use these techniques during tracking to eliminate sounds I didn't want to capture, and RX 3 really helps during mixing, especially on sessions I didn't track myself.
It can be run as a standalone application or a plug-in (AAX, RTAS/AudioSuite, VST/VST3, Audio Units). RX 3 might be perceived as an audio restoration, forensics, and post production tool - and it certainly is - but I mostly use it on recording and mixing sessions. As mastering engineer Roger Seibel said, "If it sounds better, use it." Since then, iZotope RX has become one of my most-used plug-ins, and in lieu of writing up the giant list of its features (many I've never even tried yet), I am going to explain how I use RX, and now RX 3, in the recording studio as a tracking and mixing tool. When "Angel in the Snow" required a new instrumental mix for the film Up in the Air, I used RX on the original transfers of the tape tracks and was blown away at how much better the mix sounded, enough that I snuck a new mix onto An Introduction to Elliott Smith in 2010. Not much later, I stumbled across iZotope's booth at an AES show, and after explaining my issues, I was given access to the initial version of RX Advanced.
I rented a single-ended noise-reduction plug-in from a certain DAW manufacturer, and while it did reduce the sea of tape hiss, I heard fluttery artifacts in the background. The song was beautiful, but the tape hiss was not.
One song in particular, "Angel in the Snow," had been recorded onto 1/2'' analog tape at a very low level. When I began work on what would become Elliott Smith's New Moon album in 2006, I knew I might have a few noise issues to tackle.