Have been doing printf "text" to print some text from a bash script. Is using printf without a format string valid to do?
Putting the entire message in the format string is a reasonable thing to do provided it doesn't contain any dynamic data. As long as you have full control over the string (i.e. it's either just a fixed string, or one selected from a set of fixed strings, or something like that), and you've used that control to make sure it doesn't contain any unintended escape characters, all % characters in it are doubled (making them literal, rather than format specifiers), and the string doesn't start with -.
Basically, if it's a fixed string and it doesn't obviously fail, it'll work consistently.
But if it contains any sort of dynamic data -- filenames, user-entered data, anything at all like that -- you should put format specifiers in the format string, and the dynamic data in separate arguments.
So these are ok:
printf 'Help, Help, the Globolinks!\n'
printf 'Help, Help, the %s!\n' "$monster_name"
But this is not:
printf "Help, Help, the $monster_name!\n" # Don't do this