First: What razz. said.
The reason you start with "3-3.5" metres length of beer line is that the resistance of the beer line is "using-up" the pressure from the keg. The final output pressure should be quite low relative to the serving pressure.
There's a formula to work out how much line you need. This takes the diameter of the beer line or the internal liquid "drag" of the beer line itself, the height difference between the keg & tap, the serving pressure, etc. as variables. If you plug say 5mm (ID) beer line, 1 metre, 70kpa - you get about 3 metres.
So starting with more than that, you can just test it it, and cut a bit of the end off of the pipe, if the pour pressure is too low. Thus shortening the tube to its optimal length without the mathematics.
The flow control taps allow you to use only enough tube to connect the keg to tap. Thus there's not a complete tangle of pipe in your keg fridge.