-More wear on the suspension components as it's not designed to be at the height for great distances/speeds
-Way more wear on your drive shafts as they are at a more extreme angles going much higher speeds, especially if you use extended mode off road
-More risk of roll over at higher speeds
-More tyre wear as you can't get the wheel alignment prefect at that height
-If you have a rack you can't go into under ground car parks or anywhere low(well in LA I use access mode quite a bit because a lot of car parks are less than 7')
-Worse ride quality as the airbag a much fuller which means firmer ride
-You pretty much get rid off all your wheel droop when going into extended mode not good for cross axle situations when off road as you will lift a wheel very quickly, yes Terrain Response is amazing and will lock the wheel up but you get more traction with 4 wheels on the ground compared to 3
there is probably more but I just can't think it them right now.