I've been giving some serious thought to whether I want to include any fortifications in to army lists. For the price of a rhino with havoc launcher, I could get an Aegis Defence Line for my armies. That seems reasonable -- but what are the advantages? Beyond getting a 4+ save exactly where we want it during deployment, I noticed a unique bit of wording with the Aegis Defence Line in the 6th ed rule book:
"each section [...] must be placed in contact with at least one other section"
So, we could certainly create a big circular defence line to place an important long range shooting unit behind ... or perhaps two smaller circular / rectangular sections. But since we get 8 sections, we could create four walls for our units to hide behind (see image). Each section is adjacent to one other and therefore fulfils the rules requirements.
Why is this any good? Well, the number of times I feel I've deployed on boards without sufficient cover saves in my deployment zone is large. With this strategy, I can have 4 "buildings" with a 4+ cover save (i.e. the same as ruins!) that I can shoot behind of in safety and go to ground on an objective behind all game long (i.e. 2+ cover save). The only negative is that I don't get the elevation that I would ordinarily get with multi-level ruins. This may or may not be an issue depending on the rest of the scenery across the board. I'm thinking that purchasing an aegis defence line in an army list could well be worth-while.
The other thing I've been thinking tactically about is also illustrated in the image: two sections with one in front of the other. Here's the thought: have a tarpit unit behind the first wall to engage and charging units (presumably because they're on top of an objective?) and have an all-round unit behind the second (i.e. one that does both shooting and melee). Any charging opponent will get shot at (maybe twice if they get out of a tarpit), risk a counter assault, and potentially have to assault the second unit next turn. Well ... it'd have to be set up in a "funnel" manner, but the idea is entertaining. Aerial strikes and outflanking units clearly nullify this idea pretty quickly, but against a ground assault, it'd work very well.