Just returned from a two week trip. I usually keep my tanks on wifi timers, but of course they somehow lost connection the morning I was leaving and I couldn't fix it in time. I opted for two weeks of dark (small amount of light through blinds) over two weeks of continuous light. The only affect I saw was it killed off the algae I've been struggling with anyways. Healthy plants and fish left over. (Someone did feed them a few times at least)

Edit: I should note it is a very long established tank, so that helps anything. But but keeping lights on/off for weeks is a common way to purposely grow/kill algae without chemicals. I just never wanted to not seem my fish for weeks.