I certainly adjust the mode of my lights depending on conditions. I.e. during the day I just want them to be seen, so I'll either have them off in areas with little traffic, or in bright flash mode in areas with more traffic risk. At night I still opt for the bright flash mode in areas with sufficient lighting but lots of traffic, but switch to bright-steady in areas with less lighting. And I'll switch to dim-steady on MUPs.

The battery life on my lights is sufficient that I rarely have to worry about it. But if I were doing a very long ride at night then I'd use the dimmer light setting in areas with less traffic and other light distractions (I find that relatively little light is needed in really dark areas where my eyes become dark-adapted).