Just my original question: does anyone have a reason not to use an executable packer like UPX, that is, does anyone know of any problems?

I meant does it break functionality? Like suddenly script abc.kix doesn't work anymore on machine XYZ or something like that.

I thought that was pretty clear but perhaps I should have pointed that out better. I'm not interested in a debate of whether or not to compress, the shortcomings of UPX or any packer for that matter or techniques for bandwidth preservation. Those are of course a good topics but have nothing to do with my question. Same goes, imho, for the conversation thread you mentioned earlier. Ciper's basic question as to why the increase in size over time or why the kix executables aren't compressed already in some form is not answered.

You have way too much attitude for a moderator, calm down a bit, step down from your pedestal. Nothing wrong with your knowledge, but if you'd talk to your partner in the way you answer questions here you'd be sleeping on the couch a lot.