It's pretty much your call.
If it's a pattern that looks just as good viewed top to bottom or bottoms up, go ahead and knit it as written.
If it's a pattern that has a definite direction, flip it. It should work fine for stranding, cables or intarsia; might be iffy with lace.
If it matters to you, remember that when you look down at your own socks you're seeing them upside down.