Once you go down the path, it's easy to start adding more and more, and it's easy to forget about them. They sometimes blend in well with patches you generate, since it's just a 'print()' and nothing obvious like 'import pdb; pdb.set_trace()'
People create bugs by forgetting things all the time. If you believe their spin, FB snarfed millions of contact lists by accident because of that. I've troubleshot countless things that happened because of code that fell between the cracks. And on the other side of that, I could tell you about the time we went a month without logs in production because someone didn't properly test a library change, so everyone's carefully manicured logging broke.
There's nothing wrong with print(), at least that isn't wrong with a lot of other things.
Or you can be organized and competent at a higher level and just use tools. We're using computers for a reason :)
They're very visible in diffs then. And even if accidentally committed they're still easy to spot and eliminate later.
//#DEBUG 1
#include "debug.h"