What benefit could Persians have derived form conquering Greece in the Persian War?

Answer 1

They used superior naval tactics and destroyed the Persian navy, which threatened the Greek cities and also protected their supply line.

When sea supply was lost, the Persians had to send half their army home, which evened the land forces up.

The Greeks also operated on broken ground which negated the advantage of the superior Persian cavalry.

Their infantry had armour, which gave them the edge over the unarmoured Persian infantry.

Answer 2

the Persians were greedy and wished to extend their Empire. Greece was a main key to this. it was bordered by a sea and had many other Empires surrounding it. if it was taken Persia could extend its empire throughout Europe.

Answer 3

It could have achieved its object of imposing peace on the Greek city-states and stopped their incessant wars spilling over disrupting the peace and prosperity of its empire.