Using tessellation on Landscapes causes a greater impact in performance than what is expected.
In the screenshots provided there is a comparison between tessellation disabled and flat tessellation with a zero tessellation multiplier. One would expect the latter to have lower base performance cost since the tessellation is not being utilized.
Note The user submitting this test case seems to believe this issue is also view angle dependent between the directional light source vector and the player's view angle.
Update:
Most of this feature/fixes will be available through 4.19 but some part of it will have to go in 4.20.
1. Download and Open attached project.
2. Press Play in Standalone mode.
3. Bring up the console command and enter 'Stat FPS' and 'ProfileGPU'
4. Roll out the Scene > ShadowDepths within the profile gpu dialog window.
Outcome The ms time and frame time have almost doubled
Expected There should be a small base performance cost, but not as extreme
Head over to the existing Questions & Answers thread and let us know what's up.