Having had a quick scan (I wasn’t aware there was one). It doesn’t look like there are any real benefits for end-users.
The Racing Post API is a B2B offering for affiliate websites to post up all their data. Great advertising prospect from them I guess, so it’s a smart move.
Looking at the information available via the RP API it only seems to be things like results, tipping and historic form. Ther’s a few of their ‘products’ too.
Personally I wouldn’t see any use for it unless you’re looking to sign up people to bookmakers to lose money – something we’re certainly not all about! Quite the opposite in fact.