Lightroom emphasizes the use of Collections to optimize photo organization. I have been a Folder guy, but viewing this tutorial, I plan to explore Collections once again. (Note: one feature I was not aware of is using Collections to share albums similar to Google Photos). More to explore.
Collections - 7 Reasons Why
1. Collections allow different photos from different folders to be consolidated into one collection
2. Placing the same photo in multiple Collections (i.e Sunset, Travel, etc.) do not use HD space
3. Collections allow syncing to all mobile devices
4. Collections offer a more streamlined editing process Lr-PS-Lr
5. Collections appear in all Lr Modules (emphasizing Adobe's model of Collections 'rule')
6. Collections allow you to share an album (a created collection) via a link (like Google Photos)
7. Smart Collections allow ‘automatic’ Collection selections
See the full 30-minute video 7 Reasons for Collections.