For fluff this lascannon steel legion team are squatting in the mud in the ash wastes of Armageddon. The charge pack is perched above the mud on a stone. The mud effect is made by painting liquid green stuff in a patch in the centre of the coarse sanded base
More intricate basing could be used to link models who are part of a team and add some dynamism to the base. Here the drug stim crazed missile launcher team are in the process of reloading the launcher while nearby a lasrifle has been embedded in the grass by its bayonet and a spare missile is stuck nose down into the ground. They seem to know what they are up to so perhaps the dice gods will give them a better than 50:50 chance of hitting their target.
Here another missile team squats behind some battle field wreckage. While cover for cover saves cannot be incorporated on a base perhaps the suggestion of a cover hugging squad might increase the chance of favourable save rolls? Or persuade an opponent to try for another target, forgetting that cover cannot be incorporated on to bases. For another bit of headology adding height to a minis base to make it appear more imposing or threatening might just draw fire or attention or otherwise disrupt an opponents thought processes to their disadvantage. Obviously think about how the verticaly enhanced character is to be deployed or all that attention might take them out the game early. Does basing influence players? It probably does subliminally. Is this another aspect of the metagame or is it a legal way of getting a slight advantage?