Originally posted by John:

Originally posted by Syri:

The terrain modification issues were fixed before the hearth and home update. Altering terrain now should make no difference to performance. The only exception is if you're using any mods that do terrain modification, as some of those could still be using the old system.
I've raised land out of the sea, cut a harbour into a land area, flattened a large area to build a town and re-shaped the coastline on a fair sized island, without any issues.

Wrong, depending on your hardware it influences a lot. Fighting bosses at 60 fps here, my base on the other hand, 40 fps.

Nope, not wrong. Terrain does not impact frame rates. Building however, does. If you build something it adds to the number of instances the game is handling, which can be seen by pressing F2. Changing terrain used to generate new instances for each modification, but now does not as it now removes any historic data, and only uses the current layout data for the terrain. So yes, your FPS will drop in your base, but not because of the terrain. It's because of what you've built on top of that terrain.
The building system will still have a big impact on frame rates, especially with larger builds, but the OP was asking specifically about terrain, which is all I covered in my original reply. Terrain and building are two different things.