I would like to add the phrase "Please do not use this tag for differential equations." as first line to the tag functional-equations.
Of course, differential equations ARE functional equations, but this is not the way that I have seen "functional equations" used and it corresponds to the way I want to use the tag (I am interested in answering questions on functional equations different from differential equations) and I cannot imagine someone using "functional-equations" to search for differential equations. It also seems to correspond to the use of other tags.
However, I realize that this is a question where I am not sure what other users think, so I want to give you a chance to weigh in.
Examples of questions from last week tagged functional equations:
Solving the differential equation $f'(x)=af(x+b)$,
How to solve $(f'(x+1)+f'(x-1))f(x)-(f(x+1)+f(x-1))f'(x)=0$
Reaction to answers and comments: You have made me understand why people would reasonably choose these tags. I am not 100% convinced that this is a useful thing, but since the default stance is certainly to let everyone decide on their tags, you have convinced me to do nothing.