I can't think of a good reason for a proficient matched-grip player to ever use traditional. And I say this as a guy who grew up on traditional, and still uses it occasionally.
If you already are comfortable with matched, spend your time and effort working on getting better at matched grip.
The only reason I still occasionally resort to traditional is because that grip had a 5-year head-start in my own playing. Unless you're marching in a drumline that requires traditional, I see no reason for a good matched grip player to bother with it.
Not the most popular opinion, but I'll stand behind it.
That said, you can certainly get around a kit and crash cymbals using traditional. It just takes practice.
Keith echoes almost exactly my experience and sentiments. What happened to me is that I moved to L.A. in 1980 to go to college and started to change to matched when I hit there. I had only flirted a bit with it before then. The motivating factor was that most of the guys at the school were following the wisdom that matched could transfer to different scenarios (such as multi-percussion setups and other percussion settings) and that it also gave a more homogenous and even sound between sticks when on the set. It took me a while to actually change over to matched, but I'm glad I did. It's now my strongest and more comfortable grip,
However with the recent 'Freddy Gruber' movement (started for the most part locally here in L.A.), I have gone back to practicing traditional on my pad. My experience though, is that for me to truly use the trad approach, I have to setup my kit differently,
especially the snare. Dave Weckl echoed the same thing in a conversation I had a few years ago. My approach to snare drum angle may change slightly here and there when I'm using matched. It chages greatly when I use traditional. Therefore I have to kind of commit for the night or at least the set to one or the other. Match grip typically wins.

Unless you truly want to learn traditional for your own reasons, I don't think there is a blanket, general wisdom that says you
have to or even
should.
IMHO, My .02
Jim