Mosaic tiles come on sheets rather than as individual pieces, which makes installation far more straightforward than the intricate finished pattern might suggest: you lay the sheet and grout, not tile by tile. That sheet backing also gives mosaic a structural advantage other formats do not have, flexing and bending to suit curved walls, arches, and concave or convex surfaces.
Because a mosaic has so many more grout lines than a larger tile, it also opens up more expressive grout choices, a contrasting colour will accentuate the pattern within the tile far more than it would on a plain large format surface. If you are working with a curved wall or an unusual architectural detail, mosaic is very often the format that makes the project possible in the first place.