Elevation doesn’t provide you with the same type of protection that cover offers, but it does provide a different tactical advantage. One of the main benefits of seeking higher ground is expanding the area of your line of sight.
A high vantage point allows you to shoot down at enemies who might try to duck for cover. It also allows you to go into a lower and more accurate stance while still having a commanding view of the battlefield.
In addition, the height of the structure offers some protection from enemies at close range because they can’t target you when you are above them and out of view. However, this also means you can’t shoot them if they hug the base of the structure beneath you.
Still, being on a rooftop can be a great spot to pick off foes. The height gives you superior visibility to wipe out enemies, and you can maneuver toward the center to make it difficult for enemies to hit you.
If a roof or other high spot has an edge or other form of cover, it can be even more effective, allowing you to stay low to avoid fire and pop up to unload when you are ready.
The other advantage of seeking higher elevation is that there's usually a limited number of ways to reach the perch, which forces enemies to approach you on your terms. For example, if you're on a rooftop, enemies are forced to climb a ladder to get to you.
This will leave them very vulnerable because they have to get off the ladder, pull out their weapon, and aim.
Meanwhile, your squad already has a bead on them and is in a great stance to deliver highly accurate and damaging shots. One of the downsides of being up high is that you might not have as many choices for retreat.