in wow does it matter where you fish?

Answer 1

The region (zone) determines what fish and loot you will be able to find. Besides that difference, it doesn't matter where you fish.

Answer 2

You'll be unable to fish in certain places depending on your fishing skill level. I would argue that it matters a lot where you fish. Certain areas will hold fish that are rare for crafting needs or rare fish to get fishing achievements.

Answer 3

You can fish anywhere at any level.  However, unless your fishing skill is high enough for the zone you will not recieve anything besides junk that sells for little value and has no use (grey items).

Though you can fish out of pools at any skill level and get the fish you want from it.  For instance you could fish for the Fathom Eel from Uldum with level 1 Fishing as long as you're only casting in Fathom Eel pools found around the southern beaches of the zone.