It may also make a difference if you book the Latam flight as part of a longer trip, for example on the same ticket as a BA fare to get to Brazil.
If that is the case you might get a better luggage allowance due to Interlining.
Baggage interairline | LATAM Airlines
However I am far from an expert in this and for my trips I can't book the Latam elements in the same reservation as the BA elements for other reasons so I guess I am stuck.