Profiles
When you sign up to Band Mate you get a profile. Every user has one. It is where you can enter information about yourself or your band. It's where people will go if they want to know more about you. Just because you have a profile doesn't mean that you are actively searching or offering yourself on Band Mate, that's where listings come in.
Listings
Creating a listing on Band Mate is important if you are actively seeking musicians to join you, or if you want to join other musicians. If you have a listing, other users who are either looking to join a band or are trying to recruit band members can look through all the listings and find potential matches. It's espcially useful if you are, for example, a solo musician as well as a band member, or you are in two bands or multiple side-projects. This is because listings allow you to create more of a presence on Band Mate without the need to manage multiple accounts. You can create as many listings as you want, one for every project you are involved in, or one for every band member you are seeking!
If another user likes your listing and wants to find out more about you, they will then refer to your profile.