Since 6.0 Blizzard has added a new feature called "Summons random mounts" which was inspired by third-party addons and implemented into the default UI, while being appreciated, this new feature is far from mature, summoning a random mount from a pre-defined "mount table" isn't enough in most circumstances. It does not shape-shifts a druid/shaman into Travel Form/Ghost Wolf in combat, it does not exclusively summon Abyssal Seahorse in Vashj'ir underwater, it does not allow a Druid to add his flight-form into that random "mount table", it does not even recognize the item "Magic Broom" as a mount during the Halloween weeks, in short, it does not make intelligent decisions for you.
I'm sure one day IntelliMount will become unnecessary but not today. Today you still need it to summon mounts intelligently for you, just press the hotkey, IntelliMount knows when and where, it "determines" which mount is the best choice for you at the particular moment, and summon the one for you JUST RIGHT.
Also, sometimes you may want to jump out from the random "mount table" and directly summon a special mount like X-53 Touring Rocket for carrying a friend, Traveler's Tundra Mammoth for selling junks, or Azure Water Strider for crossing a river in a non-fly zone, etc. IntelliMount simply makes all those happen.
Goto the defualt "Key Bindings" UI and set hotkeys for "summon regular mount", "summon passenger mount", "summon vendor mount", "summon water strider", then enjoy.