Thanks for your question!
Unfortunately I’m not too familiar with Adobe After Effects, but presumably compositions are a holder to help reduce clutter and make it easier to quickly add components into a scene.
When creating an experience in Studio, we suggest to make different assets and components within sub symbols.
Subsymbols are reusable ZapWorks Studio components and can be used to define functionality that is to be used more than once. A subsymbol can also be used to separate and abstract functionality away from the main root symbol. - Subsymbol Overview.
For example - If a scene was to have multiple components, all with timelines, it can get a bit confusing.
Different assets can be grouped into sub symbols along with there animations, then drag and dropped into the main scene and referenced. A main timeline would still have to be initialised but it would reduce the confusion of having all the key frames of separate components of the scene all in one timeline.
I have added a quick breakdown below to give a visual explanation of this.
Hope this helps!