Here's an example:
He's eager to please.
He's hard to please.
Traditional grammar would suggest that they are the same- s + v + adj + inf.
Tranformational grammar would show that they are very different. By turning them into the passive, we can see that they are different:
It is hard to please him (OK)
It is eager to please him (Not OK)
Henece, transformational grammar looks more deeply at how the sentence really is structured, rather than simply labelling words.