You need to turn off the router if you are careful about natural resources and want to save a little. The consumption of a modern router is about 5W per hour, which is 120W per day, 3.6 kW per month, and 43.2 kW per year. At a rate of 5 rubles for a year of continuous operation of the router, you will pay approximately 220 rubles.
Not necessary. Why do you want to do this? If you think that it is harmful, then this ordinary radio radiation is several times safer than the cellular signal from your phone. You can read more about the harm and safety of wifi here - https://wifika.ru/wifi-vredno-li.html
It is better to turn it off whenever you are not using the Internet. Here in the comments they write that the proven harmlessness of Wi Fi is nonsense. On the contrary, Wi Fi has been proven harmful for humans, and not only for humans, for any living organism.
The results of a study by American scientists - Wi-Fi routers through the emission of electromagnetic waves can increase the level of ROS (reactive oxygen species) in the body. This, in turn, leads to cellular damage through oxidation. This process creates the preconditions for the appearance of cancer cells (!!!) and malignant tumors.
I believe that you do not need to turn off the router at night.
Well, first of all, I will start with the fact that the harmlessness of the router has been proven, the main thing is not to keep it close to the reproductive organs every day.
As for saving electricity - will they save you about 168 rubles a year?
Logically, it can lead to a fire like any electrical appliance, but so far there are no statistics on fires where the source was a router.
I would advise turning it off at night if you don't trust your neighbors and traffic is limited.
Turning it off is simple - you can unplug it or press the off button on the back of your router.