Even though I have Ozone 7 and use it most of the time, I still use Ozone 4 for a few things, though usually on a channel rather than the master bus. The Multiband Dynamics in Ozone 4 includes a gate feature that isn't in 7, so you can eliminate specific frequency ranges below a certain threshold. Sometimes that's exactly what you need to remove noise & keep the sparkle on a channel. And then there's the frequency matching & morphing! Ozone 7 has this too, but Ozone 4 let you save snapshots of different songs / channels & reload the snapshots from a file later. I'd built a library of EQ curve snapshots from my favorite songs, and also of isolated tracks from commercial songs. So if you wanted your vocal to match the frequency curve of a pro isolated vocal you found, or to match the EQ of your guitar to an isolated pro guitar part, you could save a snapshot of the isolated track to your library, then use Ozone 4 to match to it... or even just show the curve as a comparison reference while you program in your own EQ with other plugins.