The Whole Roof, Including What Nobody Can Walk On
A ladder shows you one corner of one slope. Somebody leans out, takes a look at what they can reach, and comes down. Steep slopes, second-storey sections and brittle roofs often do not get inspected at all, because walking them is unsafe or would cause damage.
A drone covers every slope in about ten minutes, close enough to count shingles, and leaves you with photographs instead of an opinion.
It is also safer. Nobody is on your roof, and nobody is on a ladder against your gutters.
If you would rather just have someone look, the drone inspection is free and you keep the photographs.