French open-hole keys require that the player cover a hole in the center of the key cup. The open holes are located under the 2nd and 3rd finger of the left hand (A and G), and the 1st, 2nd, and 3rd fingers of the right hand (F, E, and D). While favored by most flutists, legitimate arguments for plateau (also called closed or covered) keys abound. I'm going to disappoint the plateau proponents, though, by limiting my discussion to the benefits of open holes. Sorry!
Open holes can be used for effects such as bending and shading, and the player can crack some holes to bring pitch back up when playing softly on high register notes. Playing open holes requires and therefore develops fingering accuracy that is not essential on plateau keys. Some clever trills make use of the open hole venting for better pitch.
Because most fine flutes are built with open holes, the selection of flutes available is many times greater. If one insists on plateau, he/she may have to special order a flute and might be required to pay before knowing if the flute meets expectations. Open hole flutes can be used as closed hole by inserting plugs in the holes. We ship all flutes this way so that a musician new to French open holes can easily play the instrument. One can remove a plug at a time until the technique and feel is developed. I recommend taking out the A first then the F. From there take out the E last, remove the 3rd fingers, either the G or D first depending on the individual. Open hole flutes being the standard, they will retain resale value also.