There's no such thing as too wide

Look at this clip of Timo Boll training:



Notice how far apart his feet are? A wider base is always better, whether you're squatting a grand or looping a table tennis ball. You're stronger and more balanced.

I've had a couple people tell me I set my feet too wide when I'm looping or returning serve. When I ask why I should adopt a shoulder-width stance, they tell me it's faster. But that's only true if your hips are weak, inflexible and unstable. The solution is to improve this weak point with split squats and wide stance squats.