As shown in the picture posted by @Ron R, the blade edge will roll with use. If you flip between each shave, you can kinda chase it around the center point. If you wait until the blade starts to lose performance before flipping, you're probably not going to get much benefit from it. Even with constant flipping, it might not extend the blade life by much, cause the blade will also be chipping and denting with use and those kinds of damage cannot be mitigated with flipping.
I personally don't bother with flipping for two reasons, 1) I only disassemble and clean my razor between blades not between shaves, and 2) for me it might get me 1 or 2 more shaves out of a blade, which would increase the expected lifespan of my current blade supply from ~12 years to to ~15-18 years. I can get the same increase from spending $10-30 on another 100 pack. I'm fine with that.
I personally don't bother with flipping for two reasons, 1) I only disassemble and clean my razor between blades not between shaves, and 2) for me it might get me 1 or 2 more shaves out of a blade, which would increase the expected lifespan of my current blade supply from ~12 years to to ~15-18 years. I can get the same increase from spending $10-30 on another 100 pack. I'm fine with that.