Assuming you will use the RMK for off trail, you definitely want to let the sled "rock" back when you gas it to take advantage of the longer track in the loose stuff. Doing that means you will steer more with weight transfer than you would with the skis which are far less effective in powder than on the trail.
On the other hand, if you intend to do more trail riding then you will want the straps to limit the rock back and keep the skis on the snow.
If nobody told you loosing the straps is not the only adjustment for your riding conditions and style. You will want to increase tension on the front shock too.