Presets allow you to save and load groups of biomes so that they can be used in other files and projects.
For example, if you spend ages creating the perfect forest landscape, and then you want to use it again in your next project, you can simply export the biomes you want to a preset, and then load it into the new file with a few clicks.
To save a preset, go to the biome list and click the dropdown next to it to open the extras menu. Then click "Save biome settings".
Then, you can input a name for your preset, and select all the biomes that you want to include in it.
Note: If you save a preset with the same name as an already existing one, it will be overwritten with the new preset.
To load a preset, instead click the "Load biome settings button".
Then select the presets you want to import and click "OK".
Note: Since presets can contain many different trees, it can't take quite a long time to import them, during which time the interface will freeze. Also, it's a good idea to make sure the object you are applying the presets to is not too big, as blender may attempt to load far too many trees and cause a crash.
If you want to delete, or change the names of certain biomes, you can do so in the manage presets panel, again accessed from the extras menu.
Here you can look inside the presets to see their contents, as well as edit their names by clicking on them, and deleting them with the bin icon.
Note: Deleting presets is permanent, and cannot be undone! You should be certain that you no longer want the biome before you continue.