Historically, edge spots have been used in casinos to assist remote camera identification of the different cash checks on the tables. And as less important no-value chips, tournament sets were most frequently created as solids, or used simple uniform edge spots across all denominations.
Personally, however....
I prefer the -look- of a well-designed progressive spot pattern for tournament chips (think ES primaries or spotted Aztars). But I've found that solids or single-spot configurations work much better in actual practice for tournament sets, mostly because the base color of each chip is so more prominently displayed.
GCR solids, both WSOP 2007 sets (and their clones/tributes), and the Aurora Star hot-stamps are great examples -- they all play very well, with easy-to-read denominations, clear and distinct color choices, and without the unnecessary confusion in pots caused by multiple colors and spot patterns. Adding multiple spot patterns to any of those sets would greatly diminish their effectiveness during play, imo.
I do have a couple of tournament sets that use just two or three different spot patterns across all denominations, and they seem to work well as a compromise between the two spot design approaches (uniform vs progressive). The ACF tournament set uses just two (614 and 8D18. eight denoms), and my semi-custom 43mm set uses 8D18, 8V, and 3D38 spots across six denoms.