Startup values is as the name says startup values. It is the first values which is send on the dmx channels.
This can be used to set all default values to the fixtures.
An example could be focus on moving heads. This will typically be adjusted during building the gig.
Here it is set to the value 41.
The whole set of data is saved as startup values.
This means that when the PC is shut down / rebooted the first value send it focus = 41 and you don’t need to adjust focus again.