Like when you send a .7z instead of a .zip or .rar to a friend or a teacher because that’s what your computer has installed and they’re like “Oh No, not one of those, now I have to install 7Zip” even though the same program that opens .rar also opens .7z I feel like people are way more annoyed when they receive a .7z
RAR5 is a nice format with a very good compressor. More efficient than 7z. However I believe 7z with lzma2 can be tuned for a better compression ratio when throwing a lot of RAM and CPU on the problem. But for day to day usage, I prefer the speed of RAR.
No, RAR5 is not more efficient than 7Z. 7Z ratio can be 5-10% better. Even the speed advantage is gone during the last couple years. RAR does have recovery record support, however, and better Unix/Windows precision timestamp support.