Powder burn in rifle barrel

[amiabledave50]

What's the consensus of the percentage of powder burn in a rifle barrel? Does this affect your powder choice? 100% of the powder is burnt as soon as the bullet leaves the muzzle? Or should it be less than 100% as a bullet leaves the muzzle?
I come across a site where people have said that 94% of the powder burnt is a sweet spot.
I never really thought of it until I came across a ballistic simulator.

 

[rsmithsr]

accuracy, case fill, pressure and then % burn, but higher is better, all else is a dirty bbl