Theoretically you could use either to ferment wort. Prior to the advent of yeast strains packaged for the homebrewer that's what you used.
That being said, "Ale" yeast allows tons of different variables in the way it ferments your wort. You can essentially find a yeast that will give you different flavor profiles, attenuation (level of fermentation), flocculation (how well the yeast settles after fermentation), temperature requirements of fermentation, alcohol tolerance and the list goes on.
Hope this helps