In my occasional interactions on Reddit it seems a very large proportion of users are on the "new" Reddit, the mobile site, or an app. I'm sure it varies by community though (especially ones that heavily use custom CSS and things that don't work on the new site).
Just as one example I can recall, you can do things that are kind of like "quote retweets" with the cross-post feature that don't really make sense on the old site (on "new Reddit" when you crosspost the original post/title are displayed in a little window so you'll see people make titles that are actually commenting on the original post and not on whatever the link actually is). On old Reddit these just show up as links to whatever the original post linked to, but with the "meta-commentary" title. More than once I've encountered one of these with confusion until a comment explained, or I thought to check the tab that shows where else the same link has been posted.
