Adjustment of the QGIS appearance

It is a strange thing, but as I noticed (you may search for the screen-shots), the most of QGIS users do not use 2 quite helpful options for customisation of the program’s appearance: the side toolbars and the background color. I don't understand why. It is irrational!

A sidebar will save space of the map canvas even if you have a square monitor just because it's thinner than a regular one, and it will save even more space for a rectangle monitor (you can calculate it by yourself).

A dark-colored (I chose gray) background will save not only your eyes (they will get tired slower) and time (in cases when you will need to determine whether this white area on a raster is a white color or a transparent area) but your money too - the monitor will consume less power.

example