yup. voltage drop. i've got about a 200' loop i'm putting in 12VDC, feeding 3 dozen
LED uplights, that go flush in pavers. 1.5" diameter.... i'm using #10 wire, and
they are only 1.2 watts each, on a 300 watt power supply.
Though LED's probably aren't as bad, voltage drop on incandescent/halogen lamps in the past could result in brighter lamps close to the supply and dimmer lamps at the end of the run, especially on only 12 volt systems whether you used boost taps or not. Of course lamps at supply end of run also ended up having shorter life.