Fungi have an extremely high surface-area-to-volume ratio. what is the advantage of this to an organism that gets most of its nutrition through absorption?

The advantage is that the larger surface area allows for more material to be transported through the cell membrane. Hyphae, the body of fungi has a high surface area to volume ratio, which makes fungi extremely well adapted to absorbing nutrients from soil and other substrates through the membrane. The nutrients can also easily and rapidly reach any part of the cells interior.