Why are textures split up?

Back in the DOS days, this helped save on disk space (and maybe RAM as well, but I think the engine might store the combined textures in memory once they're constructed?)  If you had parts of a texture that repeated, like those two boxes, or versions of a wall with or without a particular decoration where the decoration covered only a small subsection of the texture, you could save just the unique parts and construct the full image at run time.

Nowadays disk space and download times aren't at as much of a premium so people tend not to bother with the extra hassle.

I would assume that it's mainly to save on disk space, since Doom was originally released on floppy disks.

The same patches can be reused in different combinations and different positions in multiple textures e.g., those two GCRATERx patches are also used in CRATE3 and CRATWIDE.

It's also pretty handy when creating new textures, as it can save quite a lot of pixel editing time.

OTEX makes use of patches a LOT. Presumably it's so people can easily make new patch combinations, but so far I don't think anyone really has.

look inside the texturex lump for the combined assets if you want to do exporting and editing in another program. personally, i love the patch editing style and it's a lot of fun to mess with when you get how it works

Crates are a good example of this, but it's also done with Star base walls, and probably a bunch of other stuff. dos games being dos games. Less work, more art.

Thanks for the quick response guys!

I checked the TEXTUREX lump and now I understand why DOOM does the stuff it does.

I didn't really understand why DOOM's monsters were offsetted rather than placed on a bigger, static canvas. I guess it just comes down to file size.