Retractable undercarriages are fitted to helicopters for the same reason that birds fold their legs; it reduces drag. As a example when the S76A first came out there were occasions were there would be and undemanded undercarriage lowering. When it happened to me the speed dropped from 145 to 135 knots immediately. The 330 and the 332, when required to operate with the gear down would also suffer from speed and range penalties.
Skids are a waste of time when moving large passenger loads as they found out with the 214ST. There was pandemonium when it was positioning on the apron and it was soon fitted with a wheeled undercarriage, albeit, not retractable.
The problems arising with retractable undercarriages do not manifest themselves very often. Certainly not enough to worry anybody.
There was an occasion on the snowy slopes of Norway where a Gazelle fitted with skids landed an shut down. The pilot had just left the aircraft when it slid down the slope and impaled itself on a snow bank. The calls went out and the pilot's superior came out, landed on, shut down and proceeded to lambast the first pilot. At this the second Gazelle slid down the slope and mated with the first one.
We did not have the same trouble with the Pumas; slam it in hard, the wheel would break through the crust and it would rest on its belly. An the end of the day when the weather was closing in and the squaddies were retreating down the hill to be picked up the German 205s had to give up.
We, however, could nail our Pumas to the side of the hill.