What are the limits for changelings when it comes to shapeshifting?

I'm a bit confused as to what limits the changelings have. Do they have a size limit? Do they get any powers from the creature they might shift into? They must get the weight, because in S8 Ep1, Ocellus shape shifts into that large anteater bug thing and manages to knock down a large structure just by backing into it.

If they're able to have the weight of whatever they shape shift into; how come they didn't use that to their advantage when trying to overthrow the princesses in the earlier seasons before being reformed?

Maybe I'm looking too deep into it but I'm intrigued as to how their power works.

https://preview.redd.it/dzeoxj5aq0ng1.png?width=794&format=png&auto=webp&s=b8decdfaf83da9e75c753902b802395d7ecf1acd