I don't know of an all encompassing guide, but I believe when the test is for equals, such as
If([Status]="shipped",
.. then the test is case specific.
But
if(Contains([Status], "shipped"), ...
is not case sensitive.
I know that report filters are not case sensitive, nor are summary field filters.
Since case ( , ) is essentially a test on Equals, then it is case sensitive.
So my rule of thumb is that for formulas testing equals or Case, then it is case sensitive, else not case sensitive in other situations.
There has been times where is Used UPPER to ensure a match.
such as if(Upper([Status]) = "SHIPPED", true...
so I convert my data to upper case and then test against an Upper Case string.
