Yea sadly there are some tutorials out there that suggest this. I would never place the power flag connected directly to the power label. The power flag is used to signal ERC where the supply comes from if there is not some other symbol that defines this. The power label (or power symbol) however is used as a label or cross-reference (something that connects things)
My guess is that you do not need the power flag on this particular net as U4 supplies it and has the pin correctly defined as power out. (For example if U4 is a voltage regulator)
So when do you need power flags? You need a power flag to signal to ERC that a net is powered even if there is no direct connection to a symbol pin defined as power output. One example is if you supply your pcb with a generic connector. Or if you have a passive component in series to the power supply (a fuse, the inductor or resistor of a filter, …)
In such a case connect the power flag directly to the pin that is the source of power (the connector pin, the “output” of the passive, …)
See also ErrType(3): Pin connected to some others pins but no pin to drive it