When to shoot the sky ( Incense management )

Hi guys,
I don't know when I should keep my incense and when I should do the sky-shooting thing.
There is so much thing do do with incense that I never found a good moment to do it.
I have Zadako, Turtle, I've shot pig 1 or 2 times, fighting now with Granpa, and trying to defeat hitman 15.
I'm a 800k power.
Should I keep more or do you think it's a good moment to shoot the heavens ?