Would be helpful to know what bike you have. The 46/30 chainring option is often seen on gravel bikes.
this:
https://www.jensonusa.com/Shimano-GR...Speed-Crankset
is designed to provide a bit of extra chain clearance for the wider tires on gravel bikes. A standard 105 crank would not have the extra clearance or the 46/30 chainring option