Auto/Manual Precompute

If ‘Auto’ is checked from the bottom of Unity’s Lighting panel (Lighting>Scene>Auto), then this precompute will begin automatically as a background process whenever changes are made to static geometry within your scene.

However, if Auto is not selected, you will need to manually start a precompute by clicking the ‘Build’ button next to it. This will begin the precompute in much the same way, while giving you control over when this process starts.

Manually initiating a precompute will cause all aspects of your scene lighting to be evaluated and (re)computed. If you wish to selectively recalculate Reflection probes by themselves, this can be done via the drop-down menu next to the Build button (Lighting>Scene>Build).