I first heard this expression from a pot-holer (someone who climbs down into caves). He was commenting on rock climbers, free climbing and so on. He said "down here we don't free climb. If you have an accident you might have to get back through half a mile of low passages where you have to wriggle through mud, and swim through twenty feet of submerged passages. This ain't the right place to muck around.
Of course, many rock climbers would say that the face of El Capitan isn't the right place to muck around, either; though if you screw up above ground it's a lot easier for rescuers to reach you. Or at least, recover your body.
Similarly, it can be fun to try to write a routine in as few instructions as possible, write methods that use some obscure method nobody else will understand etc. It might be fun to try to break all the "rules" of programming (encapsulation, non side-effects, add what you want here). When you are working on a real system, ThisAintTheRightPlaceToMuckAround. I worked for a company that had to re-write a program that needed a minor change because of this. It was in assembler, and it had real gems, like suddenly popping the last five return addresses off the stack then performing a jump.
Assembly-language ContinuationPassingStyle. :)
Somebody was playing around on work time, and it cost....
This kind of thing happens all the time in Forth; however, it has the effect of making code easier to manage instead of harder. Although, popping more than one address off the return stack is considered bad form, so I suppose it can't compare five addresses being popped off. See ElseConsideredSmelly and look for where I talk about structured returns as an alternative to ELSE (and by extension, switch and case statements). --SamuelFalvo?