Farms get an adjacency bonus for other farms after discovering feudalism in the medieval era. This bonus increases with the discovery of replaceable parts in the atomic era.
Because of this bonus, if you have a large swath of uninterrupted rainforest, it will probably still be preferable to chop it in most situations, because a patch of adjacent farms will be more valuable than a patch of adjacent lumber mills.
However, in situations where you have a scattering of rainforest tiles mixed in with terrain types on which you cannot build farms, such as mountains or desserts, it may now be preferable to put lumber mills on those rainforests instead of replacing them with farms or mines, whereas before the patch this was not the case.
If anything, the biggest consequence to the lumbermill changes is that I will probably build many fewer mines. I'll still put mines on resources and dessert hills, but when it comes to grassland, plains, and tundra hills without resources, it makes more sense to either wait until civil engineering so I can build farms, or wait until conservation so I can plant woods and then build either a lumber mill or a national park.