It is observed that CPU usage is low when baking multiple lightmaps and overhead can be particularly high when this issue occurs.

Steps for reproduction:
1) Download the project from the link shared below
2) Ensure that lightmap resolution is set to a value above 40 texels per unit
3) Start baking and while baking, keep an eye on CPU usage in Process Explorer
4) After baking fifth lightmap, ~40% decrease in CPU usage can be observed

Notes:
- Not a regression
- Details are shared below