Bonemealing Moss

Typically bonemealing moss doesn't do anything special. It does here (Under certain conditions). These may be essential to specific parts of progression.

Nether

While in the Crimson and Warped forest Biomes, bonemealing moss surrounded by netherrack will spread the biome's respective Nylium blocks. In addition, the respective fungi and roots will generate ocassionally.

Old Growth Taiga Forest

While in the mega taiga biome, nearby Grass will be replaced with Podzol. Mushrooms will also ocassionally spawn.

Mushroom Fields

Moss in the Mushroom Fields will replace Grass will mycelium. Mushrooms will also ocassionally spawn.

Deep Dark

Moss in the deepdark will replace Deepslate with Sculk. Ocassionally Sculk shriekers, sensors, and catalysts will generate.