What do *you* use collections for?

I guess many users have their own uses for Collections.

For me, they aid quick access to photos satisfying certain criteria e.g. containing a particular keyword or taken before a certain date. These photos might be from many different folders or even different drives so their coordination is much simplified by specifying the appropriate criteria when creating a collection. Smart Collections are just saved searches and therfore, when opening one, the search is performed again which might be slow. 

The biggest drawback for me is not the concept of collections but that they cannot be organised in any way (like they can in Lightroom Classic) so if one has many collections, all one sees is a lengthy list of them in alphabetical order.

Here is Adobe's help on Collections:

https://helpx.adobe.com/bridge/using/collections-bridge.html