For the win: tank trails!
A minor fx, but effective - and another visual clue on the battlefield. Makes distant incoming tanks and their direction more obvious for example. Also, just looks cool as you drive over other tank's trails - sort a 'tracks in the dunes' feeling.
I've said this is a minor fx, but that's not entirely true.
Consider; different vehicles will need different sized tracks with different offsets. Will the vehicle need two tracks?
Each track will need to conform closely to the terrain, else clipping may occur on steep slopes - but at larger viewing distances, z-fighting may occur (we've all seen it - decals flickering on distant geometry). What sort of offset should a trail have?
What sort of polygon count should each trail max out at?
Each track will need to fade out at the farthest end, while being added to under the tank - how will I achieve that? Dynamic mesh rebuilding?
If a tank is stopped, should the track stop being built? When a tank is destroyed, should the track just disappear or fade out?
For a simple fx, there's still a lot to decide!
<edit> hopefully the refinements in red Team homebase can be seen in the background. This is at occupation level = 2. Level 3 and higher occupation sees solid walls behind the glowing 'fence'.