The web is full of sites which are designed to showcase an artist's music for various reasons. Some are designed as a portal for connecting artists and industry people and venues together. Some are focused on networking artists with each other, etc. Whatever their focus, these sites have done great and not so great things for artists.
For the artist who needs quick exposure, these sites can provide traffic from industry types. Some industry and venue people crawl these sites looking for talent. So from that perspective, it's great. But if you're looking for a place to showcase your music for a fan, these sites aren't necessarily the best. Many require memberships to view and communicate with profiles on them and the average fan shouldn't have to become a member of a site just to view a profile or talk to their favorite artist.
I'll talk specifically about one site that Spencer used to gain some traction early on in his career.
At present, I am completely angry about this site and it's blatant exploitation of unsigned artists. One such issue being that if you use them to distribute your music to iTunes or other online retailers, you're risking signing away any/all royalties because of a clever loophole they put in their Terms and Conditions that cites if you choose not to keep paying them annually to relist your song with online retailers they originally listed your song with for you, then you must pay a "termination fee" equal to $15-30 per song so they take that song off the retailers website. Here's the catch, if you choose NOT to pay them that fee to take it down, you actively surrender all your future royalties for that song as long as it is listed by them.
Beyond this nifty little gem is a caveat in song ownership that you may need to clearly understand. By uploading your music to their site, you are giving them a LICENSE to promote (use) your music however they want and they don't have to pay you for it. Nice!
So, it is very important to know the fine print of some of these sites before you use them to promote your music or show your music.
In fact, it is best for you to only provide "links" to your youtube videos or music you've uploaded to a place which you trust their intentions and let these sites just refer to your music. For example, create your own artist website, upload your music there, and use these 3rd party music sites to bring traffic to YOUR site where you have 100% control of ownership of your music and content.
Now, I will say that I have found a few performance opportunities for Spencer using sites like these, so they aren't necessarily evil sites, but you have to be very careful to read the fine print.
In general, it is always a good practice to have an artist website as the key place to keep your updated music and public information (bio, tour schedule, latest news, etc.)
At some point in the adventure of the music industry it would be wise to have an entertainment lawyer on hand to review any terms & conditions of sites like these and most definitely any contractual agreements you're being asked to sign.