Is it logic that Unity 5 when adding terrian the cpu is getting to 100% ?

From what i read the unity terrian is working to calculate and working on lights shades texture not realy sure since event before i make anything with the terrain it's starting to work and the cpu is getting high to 100%.

I found that if i uncheck in the inspector the terrain to be NOT static then the cpu is normal. The question is how important is the static and this working on the terrain ? Maybe i can make it not static work on the terrain and the game and only in the end to make it static and let it work ?

Every change i make in the terrain when the terrain is static it start to work over again and make the cpu usage 100% and everything slow.