eBay has different sites like ebay.com for US, ebay.co.uk for UK and so on.
That setting option affects which site is used to place bids because sometimes it affects certain eBay policies.

What role does this setting play in the profile?
The description reads:
"My Snipe Target field is for changing a default target site to use for sniping (i.e. where your snipe will be placed)."

I have the same country all the time.