My name is Dave btw, it's kinda weird to be called pv audio formally, but do what ya do.
Yep, that's what I do. Say the piece is to be 5" wide. If there needs to be a super fine tolerance (i.e. small bookshelf type speakers), then I will have them cut them 1" larger and I'll cut it down (literally) at home on my table saw. My saw guide measures accurately down to 1/32 off, which is good enough for me.
Now for large boards (such as in this project), I have them cut the panels ~ 1/2 to 1/4" wider. That way, I just measure the panels when I get home, center them so that there's an even overhand, and at the end, just go around the enclosure with a flush trim bit on the router. Otherwise, you end up having panels that are too short and some that are too long, which obviously means that you have monstrous gaps everywhere.