For +>, I actually can’t think of anything off hand, but +< is quite useful when you keep state in a file.

For a simple example, think of one of those visitor counter CGI scripts. You could use this to keep the counter in a simple file. When the script starts, it opens the file for writable reading; then it acquires an exclusive lock on the file; then it reads the counter, increases it by 1, seeks back to the start of the file, writes the new the value, and truncates the file; then it closes the file (thus releasing the lock).

Another use is databases, particularly files with fixed-length records; also DBM files, or the like.

Makeshifts last the longest.