The two big rings with a small third ring is called half-step plus granny. It was pretty common on touring bikes in the before the '90s. Both my brothers had touring bikes with 50x45x28 and 6-speed freewheels. This type of gearing makes sense when your freewheel cogs jumps are large, typically in the 20+% range, so that the big/middle jump of ~10% "half-steps" the freewheel. A typical freewheel used with half-step granny might be a 13-32 or 14-34 6-speed.

When your freewheel cog jumps are smaller than 20%, it gets harder to half-step and it makes more sense to use a crossover such as 52x42x30. That's why you don't see half-step+granny on today's new bikes. The 9- and 10-speed cassettes are "too tight". Also, most (all?) triple front derailers these days won't handle a half-step chainset since the inner plate will hit the inner ring unless it's 8 or 10 teeth smaller than the outer ring.