90% of the time the normal kart clutch wouldn't disengage anyway. But, when I started backing my 450 in, I turned my fastest lap times. Just enough to set the kart in the corner, and hammer it out. Maybe it comes from running dirt cars previously but this never seemed to hurt me.
When I had the most problems with mine was not being able to get on the throttle coming out. Which that night was a weird night and the kart was all over the track regardless of how I ran it in the corners.
I will say this, and some are running "rekluse" clutches in their MX engines. Does the exact thing a kart clutch does but still maintains the ability to manually clutch it. I run something else though, I have a road racing slipper in mine. I've never had it slip yet, but I think it lacks the grip on dirt to successfully engage the slipper. It's tunable I believe, but I'd have to check with my engine builder. It could be an advantage, but I doubt it.
If most kart clutches don't disengage in the corners, the engine breaking is just so minimal in the small engines it doesn't matter. It could easily be handled with a slip of the clutch, but only needed in really tight corners. Which is the only time I see any of this mattering.