The advantages of tumbling at the valve for an intake charge.
There are two distinct types of motion within the cylinder, tumble and axial swirl and it's possible to have a combination of both.
Tumble will tend to decay into smaller eddies that lose momentum as the piston approaches TDC. It will also be most apparent at the "wrong times" during the 720 degree cycle: some engines it occurs strongly around peak valve lift and in others it occurs at low inlet butterfly valve lifts.
Swirl can be imparted to the inlet charge with staggered inlet cam profiles or by valve deactivation or perhaps with port de activation. It doesn't decay as much when the piston reaches TDC and there will be plenty of motion within the cylinder when the ignition point is likely to occur.
Increased cylinder motion WILL improve combustion burn rate. However this will have minimial impact on fuel economy and performance directly. the increased motion can be MADE to work for you in terms of part load fuel economy by being able to withstand more EGR.Similar story for lean bun at part load without going so readily into misfire.
There is also a benefit to having more charge motion in during catalysts warm up- on spark ignition engines- where by alot more ignition retard can be dialed in without combustion stability decaying as much. This is invaluable when you're trying to get your car through emissions.
Detriment is that tumble or swirl illicited solely by the intake ports WILL have a negative effect on full load performance- whereby momentum is being used up in the charge motion within the cylinder- rather than getting the air in.A varaible device of some sort would be helpful and indeed many have been patented.

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