It is used but not limited to just a simple way of saying "let's go",
it is also used in a situation when a quick escape or exit is a must.
It can also be used in a story to descirbe somthing that you have done or somthing that has happend to someone in a past tense situation.
Gary: This party is shit.
Jimmy: Yeah you're right. Blowydog?
Gary : Fuck yes!
Gary: Oi this chick im meeting up with has a friend with her. You keen?
Jimmy: Fuck yeah!
Girl: Hey you're friend should come meet my friend over here.
Gary: yeah sounds good.
Girl: Hey Jimmy this is my friend.
Girl #2 (who turns out to be a fatty) Hi jimmy nice to meet you
Jimmy: (turns and looks at Gary) Blowydog.
They leave in a speedy fashion.
Example 2 (continued)
Daniel: Hurry up and piss cunt!
Johnny: (who is pissing on a shopfront after a night in town) Relax man.
The police arrive
police: Oi you!!
They both run away
Jimmy: I was out the other night with Gary and he tried to hook me up with this girl... Turns out she was a fatty so I blowydogged her.
Example three cont
Daniel: me and Johnny went out the other night. Johnny was doing a piss in the street and cops pulled up, so we blowydogged them.
Jayce: I was at this party and I stole this blokes phone. He caught me in the act, so I blowydogged him. ( Jayce ran away)
Oliver: I got blowydogged by this guy at this party the other night. I caught him taking my phone and he ran off.