Biomes are a big part of making a landscape not boring. There's also a great way to introduce new flora/fauna without just adding it to already existing areas and disincentivizing exploring the world. It should be noted that biomes will only appear in newly generated portions of the map.

Learn more about biomes and how to register them in the Minetest lua API.

Code I used in the video:

minetest.register_biome({
   name = 'test biome',
   node_dust = 'default:snow',
   node_top = 'default:wood',
   depth_top = 6,
   node_filler = 'default:coalblock',
   depth_filler = 15,
   node_stone = 'default:sand',
   y_max = 160,
   y_min = -2000,
   vertical_blend = 10,
   heat_point = 20,
   humidity_point = 70,
})

minetest.register_biome({
   name = 'test2 biome',
   node_dust = 'default:goldblock',
   node_top = 'default:diamondblock',
   depth_top = 1,
   node_filler = 'default:mese_block',
   depth_filler = 1,
   node_stone = 'default:lava_source',
   y_max = 100,
   y_min = -100,
   heat_point = 21,
   humidity_point = 71,
   node_water = 'default:gravel',
})