Content profile vs profile
With the core user profile you can have just one profile.

Profile2 gives you the permission to create different profile type and with the permission you can relate it to the role.
Every profile can have different fields.
Quick example:

Let's say you have a football website, so you have different profiles for different role player like goalkeeper wing, midfilder etc...

You create one profile per each role with different fields with Profile2
goalkeeper: height, gloves size etc...

Wing: first foot, side, speed etc...

You go to people->permission->role and you create a role per each role player and then you give the permission to a role for the related Profile so user with wing role can use the wing profile.

In the core user account you can create a field "Role player" (a radio button in this case is better)

Goal Keeper | Wing etc...

Then you will use "Rules" to create the rule

React on event = After saving a new user account

Condition = data comparision (you should look for you field "role player" in core user account)

Action = Add user role (you can select the relative role)

Automatically the role is assigned.