Professionally engineered antenna systems often work at one frequency. Baluns can work very well when they are working with resonant antennas. that is, with no reactive part of the feed point impedance. They work less well when the frequency is varied from the resonant Amateur antennas often work well, with no bad effects without a balun. If there are unwanted effects, a balun might fix them. Bad effects seem to happen most often when high power is being used. A simple dipole is a good enough match to 50 ohms, so doesn't need impedance transformation. A balun will give interesting transformations when the antenna is off resonance. The outer of the coax coming down affects the radiation pattern, when the antenna is modeled. In the real world, if the antenna is not particularly high, that doesn't matter: there are usually other real world objects which have more influence. Coiling the coax into a "choke balun" might be all that's needed to get rid of RF in the shack if that happens.