Get yor point it has some right obscure stuff on it, but at the same time, nee bands the ike of tame impala, cirst aid kit, slow readers clut et al woud never get airedon comercial channels or radio 1 & 2 (6 is often called radio 2's companion station where the stuff it would play but doesn't is aired).
Also bar the odd time on Radio X , old classics like the chameleons are payed, early pulp before thet were on totp, stone roses songs that aren't fools gold, some new fads and man from delmonte, along with northern soul, ska, goth and other scenes not of interest to comercial radio.
with capital, heart, 103, you can guess the 20 same songs they will play at least 3 times in a day as required.
6 ain't perfect but I would never have heard of some of the non pop mainstream bands of the last few years without it.