I've never seen Transformers....the cartoons or the movies.
But why the intercourse would you ever turn yourself into a semi-truck if you could just be a badass giant robot all the time?
Because the life of a badass giant robot is a lonely one. Sometimes you just need love, even if it's from a creepy middle aged man with eyes tattood on the back of his head. Enough about me.
So other super badass robots would underestimate you enough to kick their ass.
Because they're robots in disguise