Limited experience with the binary repo but here goes.
I switched over a samba and sftp file server that I don’t need to customise with use flags. Along with installing and configuring gentoo-update from the guru repo to handle updates this box pretty much looks after itself now except for kernel updates/reboots and config updates which I need to look in to. I noticed when I enabled the binary repo and updated the system that a lot of packages if not most were available as binaries.
I switched over a desktop system that is basically a tv these days (it’s an old dell aio with ok speakers etc). This box has plasma installed and I noticed that some packages don’t appear to be included in the binary repo such as the infamous qtwebengine. I say appear because I haven’t delved too far into it. I can always exclude the packages that pull in this and other bottlenecks if I want so I might go down that route eventually. Again, a lot of packages just get installed from the binary repo if they are available but I couldn’t tell you percentage wise or which ones.