Long playlists? I'm all for them. They're like listening to the radio without cheesey DJs or adverts in between tracks.
It's good for specific genres, or even music to suit your surroundings. For example my After Dark playlists are easy to listen to- well- after dark of course, or if you don't want anything too heavy playing in the background (and you like your top quality music from the 60s to present day stuff) have a listen.
Best played on Spotify Premium (High Quality), and like all music, the best audio you can afford.