When putting together a large RAR file that's been split into smaller files, one can use PAR and PAR2 files to repair and replace damaged or missing segments.
You can do this with any archive format - it's not unique to RAR
I think most other formats/software support things like splitting, "healing" archives and self-extracting archives by now, so the only reason I could think of is getting the "premium support" where you can quickly reach a human to help you with whatever problem you have. That might be more important for larger companies rather than individuals.
Who needs support for archives? I don’t think they’d help in the only case I can think of: corrupted files.
If you have an tar with compression and you only need one file in the middle it will takes times.
Same problem exists with every compression like bzip2 that can compress only one file and requires an tar for multi file.
Back in the day you would hope for rar/par if you were downloading something big, like a program you couldn't afford but needed to try, I'll leave it at that.
RAR has recovery options, but it's propietary sadly.
You get to sound like a pirate.
Usenet
First law of u***net, is you don't talk about u***net