What is an advantage of a 5/8 wavelength whip antenna for VHF or UHF mobile service?

A 5/8-wavelength whip antenna is physically longer than a standard 1/4-wavelength whip. Because of its specific electrical length and resulting radiation pattern, a 5/8-wave antenna focuses more of its radiated energy horizontally, closer to the horizon. This lowered angle of radiation increases the effective signal strength (gain) along the ground. This is highly desirable for VHF/UHF mobile communications where stations are trying to reach terrestrial repeaters or other mobile stations. A standard 1/4-wave whip directs more energy upward at a higher angle, which is largely wasted in space. While it provides more gain than a 1/4-wave antenna, the distractor claiming it has "10 times the power gain" is a massive exaggeration. It also cannot magically eliminate distortion from reflected signals (multipath).