I don't, when it's sunny but I wear a bright top / jacket and my bike is a bright color and riding a bit in the road so you're not hidden in the side.

I do when it's cloudy, overcast, rainy, dark or the sun is low.

I also carry a spare light if it's a usb charged one and for my rear I have battery powered backup and I'll test my lights the night before

In pitch black riding I also add a fluorescent tabard with sliver reflective strips on