Power efficiency with Boost vs Buck-Boost using same regulator
The buck-boost circuit in the data sheet that you may be using is this one: -

Note that it uses a transformer to transfer power to the output (in red). Transformers will be about twice the inefficiency of a single inductor used in a boost circuit: -

And, in any type of power converter like this, it will be the wound components that are likely to be the most wasteful of power hence, the buck-boost circuit shown above will be significantly less efficient than the boost converter.