Generally it affects your total-shots and shots-on-goal ratio.

I'm sure there are several ways to consider it:
If you have excellent shooters in midfield - shoot near goal.
If you want your strikers to take most of the shots - shoot when safe.
If you use "near goal", but 50% or more is missing target - try "only when safe".
If you use "only when safe", but hardly produce any chances - try "near goal".

Personally I switch between the 2 depending on opposition. And I use "shoot at will" if the other team has a bad keeper, or if I just don't care [like if I'm up by 3 ].

But I guess you can also consider this:
if the other team has a huge defensive line, and a much stronger midfield than you, perhaps "shoot at will" is the way to go?