Poop where?

If it just makes spaghetti randomly somewhere not on the build plate, a) it'll leave quite a mess that would need cleaned up and b) it can end up where it shouldn't be. In a belt gear or incorporated into the print in a way that sticks out and looks bad or stuck to the hot end in a big gob that causes it to not extrude right and blob up in the print or some such.

I suppose, depending on the other print settings, it might make sense use purged plastic to make up infill. That said, I don't have any direct experience with multiple extrusion, so maybe that is a thing. Maybe slicers already do that to some extent but infill doesn't typically take enough filament to fully purge and the tower is still necessary.

All that said, I don't think just making spaghetti would work out very well.