The biggest advantage of larger diameter curves is that you can run longer trains. The original 42" diameter curves were designed with trains limited to only a few cars in mind. 72" and 87" curves allow dozens of cars to be pulled without problems.
If you like MESG (Modern Era Standard Gauge) trains, 72" and larger curves may be required. The wonderful Lionel Hiawatha and Vanderbilt sets require 72" curves as the minimum. To provide adequate clearance for these larger trains, 87" curves are required outside of the 72" curves on dual tracks.
Kirk
