Would you use it in a combat situation? Well, the percentage is low, but, as Sensei Andrew says, and it is my favorite quote from him, "The issue is not should you use it, but can you use it. And the answer is yes."
Personally, I love what the cross stance develops in solid balance-stance foundation and good footwork.
There's a metaphor here waiting to be exploited! Sometimes when things cross, it can cause uncertainty, unclarity, lack of balance, lack of focus and an unease. The cross stance asks you to find clarity and focus in the cross. It asks you to try to find certainty in what seems uncertain. It asks you to find stability in the seemingly unstable.
There are 6 types of cross stances:
1. Twist/stomp cross
2. Turning cross
3. Step over cross moving forward
4. Step over cross moving backward
5. Step behind cross moving forward
6. Step behind cross moving backward
The cross stance is definitely a transitional stance, but it can also be a "finishing" stance, and that's where I think even many Kung-Fu schools don't necessarily put their focus on. I have found/am finding that if we practice the cross stance as a "finishing" stance, doing it as a transitional stance will make it a much more powerful and meaningful experience....you will start seeing and realizing applications even in (seemingly) transitory movements, and your intent in your execution will reflect it.
Incidentally, practicing cross stances as finishing stances totally improves the attention to all the little details that go behind a complex stance.
Sensei Andrew (once again) blew my mind and demonstrated a ground grappling application of the cross stance, and I totally forgot it! I just remember being shocked, and was like, HOLY CRAP!
Incidentally, I'm looking into opening up two more Adult Kung-Fu classes in 2009.