What was the advantage of having Greek colonies spread along the coastlines of the Mediterranean Sea?

The main advantage was that they could dominate the trade across the whole Mediterranean, thus strengthening their influence and spreading Greek civilization.

Explanation:

The Greek colonization was an organized process that lasted between 8th and 6th Century BC. It was started because of the over-population, but it had large consequences on the spreading of Greek influence in the Mediterranean.

Many colonies, which were source of colonies remained in close ties with their motherlands.

b. sec, foreign relations