When to load GCPs

I see articles saying to add GCPs before running Step 1, but not an explanation why. What affect is there to adding GCPs into the project before or after Step 1? Thank you

Hello there,
There is no affect on adding GCPs, either before step 1 or after processing Step 1. If you add the GCPs before step 1, it will help to align the project with the GCPs. However, marking GCPs might be difficult if you do before processing step 1. So, normal workflow would be marking 3-4 GCPs and 3-4 images per GCPs before starting processing. Then, process step 1, mark all the GCPs and mark 8-12 images per GCPs.