If you create, for exemple, this command:

"/tp @e[type=Zombie]

@p" (No quotes and in one line, bug in this site).

This command doesn't work because it's teleport ALL zombies, not only baby Zombies, to nearest player.

Same problem for specific item, specific colored Sheep, enchanted items or mobs, mobs with effect, mobs with equipment or items, stacked entities, etc...

Only /testfor and /summon commands can support NBT Data Tags.