Wiping to avoid dripping from the travel.

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.

My experience in manually changing filament on my old printer. : There was often tiny gaps between color layers that ultimately made the model weak. Sometimes blobs instead.

(I would pause and change filament at a specific layer to get a multicolor print without a multicolor printer).

To solve this I would add a cylinder object to the plate so that the first place the head went after a color change was to the cylinder to get the filament back up to the right flow rate.

The pressure changes from changing filament is why the printer usually does a quick line at the start of a print. And why it's necessary for multicolor changes.

I don't see the full reason anywhere in the thread; the prime tower is essential to quality multicolour prints. Purging quickly shoots out a high volume of filament to quickly clear as much of the previous colour as possible, but then when it goes to start printing, the temperature and pressure are all out of whack and you get inconsistent flow.

So, if you skip the prime tower, you'll get globby over extrusions and gaps from under extrusion on the first thing printed in that colour each layer, which looks terrible.

That said, the prime tower can be much smaller than default. I set mine to 3mm³ of priming and it comes out 95-100% perfect, with only very occasional blobs on the edge, which pop right off with a fingernail flick (or a deburring tool, if you're fancy.)

Don't skip the prime tower. I did for a few weeks before cluing in to why I was getting 1 bad print on every plate.

I suppose if you're changing filament by layer, then you could maybe skip it, but then definitely don't print outer wall first or you won't get a clean print. But even then, a 3mm³ prime tower is tiny, so why risk it?

Hell, even the Snapmaker U1 uses a prime tower, and it has 4 hot ends; it's needed to normalize the flow after a temperature/flow change (being idle). I don't have one to test, but I expect it would greatly benefit from a bigger prime tower, since it hasn't just been extruding filament as purge to get things flowing. But that's just speculation, as I sadly don't have one to test with.

In a nutshell, the prime tower lets the printer print a basic shape, and if it doesn't look right, either you or the printer (depending on the model) can stop the print. It also it ensures that filament is flowing right between each layer change.

edit: Fixed. The first point seems to be incorrect, but the second one is okay