What was an advanage of Sparta during the Peloponnesian War?

Answer 1

Sparta , being a land-based power had the advantage , initially , of having interior lines whereas Athens being a naval power lacked this advantage .

[Interior lines is a strategy of warfare that is based on the concept that lines of movement, communication, and supply within an area are shorter than those on the outside.]

More:

In the later stages of the war, Persia provided funds to the Spartan alliance which enable them to build up a navy to match the hiterto superior Athenian navy. It also allowed the Spartan side to double the pay of rowers and sailors, which attracted the better ones to the Spartan fleet. Athens' naval supremacy was gone, and it had to stay within its city walls where it was starved into submission.