In AH, ground effect is also present on objects such as buildings or trees or a CV. You can notice it when you have a high bank angle during a low alt horizontal turn with a very slow descend rate (if you do it with the outside view, it will not be noticeable). As the inside wing nears the ground (not more than around 5-10ft for most fighters) it will induce a slight roll and slowly bring you back level without compensation. In short, its pretty much a proximity or surface effect. When one of your wing passes just over a mountain/hill top at high speed for example, you will feel a slight "woosh" described by a roll in opposite direction of the affected wing. Try it in the 190 and compare with the Tempest, they will be affected very noticeably.
Some of us air racers have witnessed this effect multiple times because we are used to fly awfully close to ground/object obstacles. When you feel an induced ground effect while you pass an obstacle/turn marker, that means its too close. Same applies for deck fighting.
As for increasing max take off load or decreasing landing speed etc, well... its all pretty obvious.
WW1 aircraft's (or any bi/tri-planes) wings are limited in vertical offset separation in part because of this effect.
