[cguess]

You can intercept and modify messages on the fly. This helps a lot if you want to update legacy code, but don't want to break other classes that use the same call. It also allows for modularization more easily. I have a project that receives data from a bunch of sources, so I have a class for each source (this is simplified). To make it much easier to add a new one, which happens pretty regularly, the code that calls the processor checks all the classes in a specific folder for a certain function (`.respond_to?`) and then gets the right one for the data type. This means that to add a new source I have to change 0 lines of legacy code, just drop the new class file in the right place and it works.