It's to make code more concise. There are many idiomatic one liners to compare arrays for example or to find the first element which satisfies the condition etc.
I don't mind removing them but their usecase is obvious: make the code more concise and more readable (and yes, if you program in C on daily basis you don't require a double take or thinking about what ++ does).
IMHO, these operators are the worst features of C. Particularly I never understand the necessity of both i++ and ++i operators in language at the same time.