CPU and memory usage rose sharply from Unity 4.5.3f3 to Unity 5.0 beta 2, and again in Unity 5.0 beta 8.

Using Unity 5.0 beta 8 adding a terrain to an empty scene causes CPU usage of the Unity process to fluctuate between 200% and 600%, and RAM usage of the Unity fluctuates between 1.2 GB and 1.8 GB. This behaviour was seen by watching Activity Monitor for five minutes after creating the terrain. During this time interval there was no other user interaction with the Unity editor other than creation of the single terrain.

Creating a single terrain in a new empty scene using Unity 5.0 beta 2 caused the Unity process to fluctuate between 30% and 300% CPU usage and from 30 MB to over 1 GB RAM during a five minute interval, though by the end of this interval it had stabilized to the lower values within these ranges (steady CPU usage of 30% and RAM usage of 300 MB).

Creating a new scene and adding a single terrain using Unity 4.5.3f3 exhibits steady CPU usage of around 9% and stable memory usage at around 190 MB. This is less than Unity 5.0 beta 8 uses when you create a new project, prior to creating any objects other than the default camera, light, and skybox, which takes 15% CPU and 280 MB RAM.