It offers alternatives where the choice does not matter: blow the whistle already, or at least be consistent about it; eat some kimchi or whatever. Attached to a question word it forms the very common set words 얼마든지, meaning as much as you like, and 언제든지, meaning any time, both of which appear here. Thrown out alone as a command it sounds curt, close to take it if you want.
Register: everyday; the standalone command sounds curt