adding one aspect here: I tend to use IRs to have more consistency across different rigs - easier to combine multiple amps (clean, dirty mid-gain, high-gain) for a gig and not have to suffer from sonic whiplash...
I pick a "generalist" speaker IR that works well with a broad range of amp types (fender-y, marshall-y vox-y) and use DI or merged profiles. I get the difference in feel across the amps, but retain a more homogenous sound characteristic across them. This way I can use profiles from different sources / vendors and make them play together nicely.
The other advantage: this helps me with consistency across my recording setup (mostly plugins and IRs) and live setup (Kemper / QC). I can just pick the cab IRs that work best in the finished mix and transplant them to my live setup.
BTW: My main sources for IRs are currently SuperCabinet by Overloud and Mikko2 by ML Soundlabs - both allow you to "mix" your own cab from multiple cab and mic IRs and export the result to an IR that I can use elsewhere. Beyond this, there is Ownhammer's Rockbox that I've come to like a lot recently.