We had a performance issue with DataGridViews where the redraw was horridly slow and found the solution Here to create a derived type and enable double buffering on the control. (Derived type is necessary since the DoubleBuffered property is protected)
It doesn't seem like there's any drawback to having the DoubleBuffered property set to true.
Double buffering by definition uses two buffers and twice the memory for rendering the view of the control into. So, there is some drawback there, however, with the amount of memory you get in a PC now, not many people probably would notice the sacrifice.
No idea why its protected. Maybe the function wasn't available in an early version of the control, and when it was introduced the designers didn't want to change the public interface of the control. Or perhaps they considered it to be an advanced feature and wanted to limit the number of methods someone new to the control would have to grok to be able to make it do something useful.
It is protected because DGV inherits the property from Control. And Control.DoubleBuffered is protected. Which makes sense because each derived control should decide for itself to turn that on. And it doesn't make sense for the control user to arbitrarily turn it on or off. The DGV designers decided for off.
One reason they might have decided that is that double buffering actually makes painting slower. The extra step to render the buffer bitmap costs time. It just looks faster to the human eye, you observe the bitmap suddenly appearing. You can't see the time it takes to draw into the bitmap. Unless other controls need to be painted and they get their turn after the DGV, then it is quite visible.
What you see is the form getting drawn first, with holes where the controls go. Those holes have a white background. Black when you use the TransparencyKey or Opacity property. Each control then gets the Paint event and the holes are filled one-by-one. That effect is perceived as flicker too by the user, although it is a different kind of flicker from the one that DoubleBuffered solves. It is especially noticeable when the background is black.
What's needed to solve this problem is that the entire form, with all its controls, is double-buffered. That's not available in Windows Forms. However, Windows XP and later actually support this. Check this thread to see how that's done. Beware that it can have side-effects as documented in that thread.
Inheritance is not needed to turn on doublebuffering on a datagridview. You can do it with reflection on an existing datagridview.