If you're a big star that gets a lot of radio burn and have a bunch of recognizable material that may get a lot of third party play (in sports arenas and other public settings, movie, tv, and commercial placements etc.), or have a catalog that will see significant sales years and years after the initial release (or can even be very profitable if rereleased) then owning your masters can be VERY important and valuable...basically you own the rights to your music and not the label..and if you're a big successful act, there's a great deal of actual money and value in them, they end up being a pretty big asset...it's pretty much nonexistent in modern label deals at this point, which was why cash money owning their masters as part of their distribution deal is such a big deal...otherwise if you want them, you'll have to buy them from the label at a considerable price depending on the act...
we've seen people's masters used as an asset to pay off debt, when no limit and death row went bankrupt their masters were sold off to settle the debt those companies found themselves in...which is why you see these new death row albums coming out from that new janky ass label...no limit, not so much because while they sold a lot of records in their hey day...the catalog doesn't seem to be that profitable from a legacy standpoint...they didn't have the iconic mainstream hits that deathrow did (the demand for a random song from DoggyStyle to be included in a movie is a lot more than some random track from Charge It 2 Da Game)...which brings me to another point, at the low end...far as owning your masters go its prolly a tad bit overrated in hip hop circles...if you're an independent artist with no hits and never blows up on a major level, in all reality your masters ain't gonna be worth shyt more than sentimental value anyway....like you'll see these no name mixtape rappers sometime talking this "I'm not signing to no major because I want to own my masters" stuff when them shyts ain't gonna be making him no money 10 years from now when not a single fukk is given bout him or his music anymore

....so on the high-end, very important...in the low-end, not so much