I'll start.
I've been doing repair for awhile now, and can't believe it took me this long to figure this out....
In treating customer water damage, the display will often have white spots from liquid trapped in the layers of the backlight. In the past, I've just switched out the display and the customer then has to pay for a new screen in addition to the water damage repair.
Last week my pea brain realized that I could just pull the backlight off the wet screen by desoldering the little backlight flex on the screen assembly, and then switch it out for a perfectly functional backlight from my pile of cracked screens. This was very straightforward, and for my customer's 5S, it really helped to keep the cost down on her water damage repair.
I'm sure most of you guys have been doing this for years, so it is hardly news----but, what is your "pea brain moment"?