Any reason for specifying -type f in find when looking for files with SUID bit set?

What's the reason for using

-type f

with

/ -perm -u=s -type f 2>/dev/null

. I see this all over the Internet and don't understand why to specify the type as regular file if look for SUID bit set. SUID can be set only of files and not directories so why

-type f

? Or am I missing something ?