As you browse the network and come across creator portfolios that you like, it's helpful to be able to come back to those portfolios later. There are two ways to do this: rosters and tags.
A roster is an organization-wide list of favorites, and your roster can be used to set up certain automations such as automatically assigning creators who apply to your project and are on your roster; of course, this is optional, and rosters come in handy without auto-assignment, as well.
A tag is used as a custom label to create specific lists of creators. For example, you may have multiple brands and tag creators differently depending on which brand they'd be a great fit for. Or, you might tag them based on a certain campaign you have coming up.