haven't tried it, butmy guess would be, there is a condition under which this field is required..e-g- sleeve color selection is required when color is red..or something similar

it should be that this option can be filled with the name of another (single) field X and it requires that current field will be required if X has any value

You're right, that's just how it works!

I've just used it to create a form with lots of field, many required but hidden according to an option, so it was the case to select that field to be the required one to enable the restriction.

Has anyone figured this out? I could really use a solution where a field is required if the value of another field is X.

E.g. make the field "URL" required if the user selected "Image from URL" in field 'Media Type' ... if that's what the "Yes (only when...)" option for required is for, I'd love to know what to enter in the 'Field' parameter that displays when this option is selected.