I use labels extensively in ProtonMail, almost completely over a typical folder structure, because it allows me to avoid duplication of common subfolders. Currently, most of my folders are broken down by year subfolders, and I'd much prefer just using a label so I'm not forced to filter by the year and going into each of those folders to find something if I, say, forgot which year X happened.

In general, I use folders for exclusive categories and labels for anything that may describe files in multiple folders, and I'd like to continue that structure from ProtonMail into ProtonDrive.