These RAR archives can be a bloody nuisance.
The minimal benefit in compression is offset by the fact that standard ZIP support is available to everyone using Windows. And worse yet they seem to be most popular with the most hopeless question threads, probably in part because RAR is so popular among script kiddies - most likely because it makes spanning easier for warez downloaders.
Can't we just disallow posting of RAR files instead of contrantly suggesting that if a person wants help a ZIP will reach a much larger audience?
It is very difficult to see a downside to this.