So licences can relate to a particular work, or for a particular use of a particular work. We call this a transactional licence. It's a one-time use. On the other hand, most collective societies aren't interested in licensing uses by the work. Rather, what they prefer to do is license the whole repertoire of all of the members of the collective, all the rights holders that have joined the collective. This presents significant advantages to users as well, especially in the educational sphere where schools need access to large bodies of works and it would just be too costly to try to negotiate on a piecemeal basis for the utilization of the work.
The last kind of licence is the compulsory licence where the rights holder doesn't have an exclusive right but a right through remuneration only, in which case the copyright board establishes the tariff. Again, it's typically for a broad repertoire of works, a repertoire administered by a collective society.
So there's a wide range of ways in which a rights holder can actually exercise their rights. They're not obliged to join collective societies. They do so because it's beneficial to them. But in the new world, in a digital world, some rights holders are finding that they do want to administer their rights themselves through online licensing arrangements, and that's fine too. The act can accommodate all.