Smartphones have a lot to do with the decline of fill flash. Their wimpy LED lights are no match for intense outdoor lighting. Additionally, many mirrorless cameras don't have a built-in flash. So even if you wanted to use a strobe, you probably don't have one handy.
The problem is, there are many lighting situations where fill flash will improve your pictures. And with so many affordable external units on the market, such as the retro Godox Lux Senior, it's not a deal breaker to have a compact unit available when needed.
Plus, some cameras do have built-in flashes, such as the popular Fujifilm X100V.
So let's take a look at those situations where fill flash can improve your pictures.
Intense backlighting can fool the best of camera meters, resulting in an underexposed subject. And if you spot meter just on the subject's face, then the entire background gets totally blown out.
But, if you let the camera dictate the exposure, then add a fill flash, you get both background and subject, plus a nice twinkle in the eyes.
Strong Side Lighting
When sunlight is pouring in from the side, it's not a good look for people shots. And sometimes you can't reposition the subjects, such as events like wedding receptions. Fortunately, adding fill flash will balance out the lighting.
This is a situation where built-in flashes, such as the one included in the X100V, can do an excellent job. I recommend using flash exposure compensation to dial back the output to -0.7. That provides a more natural look.
Brighten Up Dull Lighting
When your subject is in shade, the lighting is even, but can be somewhat dull. You can brighten up expressions with a bit of fill flash, as shown above. Again, dial down the output a bit to render a more natural portrait.
Using a flash can help us solve difficult lighting problems. But just as important, supplemental lighting makes our subjects look good. And that's why I think it's a technique worth exploring.