Instead of talking and everyone hearing you at the same volume level, if you are far away from someone you'll hear them much quieter.
Imagine being the captain and hearing your crew call out enemy positions from where they're standing (the port/starboard sides), or a crew member repairing the engines and calling out that he needs help. It'd definitely help the sense of realism.
Even cooler: radios or talking funnels/tubes on big ships. The Galleon could have one or two next to him and when the gunner below deck talks, it would come out from the funnel next to him.
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Voice proximity isn't a big thing in gaming, which disappoints me, but it does exist in some games. Most notably Resistance and Liberation, a realistic WWII FPS, Planetside 2 (a huge MMO FPS) and some others.