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I think it's all a matter of preference. I've always smoked mine together and did the separating after the smoke which provided some pulled brisket (from the point) and some sliced meat from the flat.
Like Laurel said, it's a matter of preference. Some people separate before the smoke especially if they are going to make burnt ends from the point.
I think the next packer I do, I will separate before the smoke. I had every intention of doing burnt ends yesterday but when it was time to take the brisket off, I had a lot of things going on didn't want to stop and separate the point before coolering it. And after the rest, the point usually won't hold together enough to cube.
About three weeks ago I did a brisket, trying out several new things. One, I separated both pieces for the first time. Thought it cooked up nicer, in shorter time and gave up more burnt ends.
Around here packer cuts is what is always available and I'm thinking that from now on to separate the two. Just liked it better that way.
Couldn't hurt to separate, you could even try it two different way if you did that.
I'm sure it will be delicious either way, be sure to keep us posted.