Lighting bakes are done on a very small texture and only one texture sheet per asset. For a single 4k PBR texture with alpha (and more mask maps in case you want moss or snow or whatever) you could have around 8x4(plus any extra masks) for 512 or 4x4(plus any extra maps) 1k lightmaps. Not to mention lightmaps are simple 0 to 255 channel rather than 3x255 for rgb.
Besides dynamic lights are used whenever performance allows making the savings smaller.
Lighting bakes are done on a very small texture and only one texture sheet per asset. For a single 4k PBR texture with alpha (and more mask maps in case you want moss or snow or whatever) you could have around 8x4(plus any extra masks) for 512 or 4x4(plus any extra maps) 1k lightmaps. Not to mention lightmaps are simple 0 to 255 channel rather than 3x255 for rgb. Besides dynamic lights are used whenever performance allows making the savings smaller.