It makes sense if you want to concatenate strings, which is probably pretty much what happens when you type that into the path input.

This way, you could create a string like "D:/%appdata%/local/minecraft" Whereas without the trailing %, you would need a space to separate it from the text, which would result in "D:/Users/Public/AppData /local/minecraft".

(i havent used windows in a while and those paths are from memory, they might be wrong)

Technically $foo also delimits at both ends, the second character is just a newline or whitespace character. However with %foo% it is unambiguous where the variable begins and ends.

Also I said newline or whitespace, what about special characters?

Look at $foo+$bar am I adding two variables together? Is the first variable $foo or $foo+?

Windows also has a language that denotes variables with the dollar as well (powershell). Or you can use bash too