Article By Jimmy McIntyre
Thank you to Phlearn for this concise tutorial, demonstrating the difference between Flow and Opacity in Photoshop. In digital blending I believe it is best to keep Flow at 100% while only changing the Opacity. Otherwise, if you’re brushing through a luminosity mask selection and you go over the same area in the same pass, you may end up with uneven areas light.
I think Phlearn is one of the best photography learning sources around. I encourage you to check out their awesome courses: Phlearn Photoshop Courses