When I did the voltage drop calculations on 20m SWA assuming a max load of 32A, I found that the voltage drop exceeded 2% for 6mm2 so that was why I ended up with 10mm2 SWA in a trench across the lawn along with 25mm MDPE pipe.

For now it's for a wood shed and a greenhouse and garden lighting and garden sockets.

There is also now spare capacity for a hot tub on the patio at the bottom of the garden if SWMBO or the rugrat so desires!

Also we may one day convert house integral garage to living accommodation so we would build a replacement garage at bottom of the garden and as water and power is already there... I currently appreciate the hot water I have on tap on the garage sink!