It seems that I'm old (my last good bike had a 5-speed freewheel and shifters mounted on down tube braze-ons - they were indexed, though!), and I've been out of cycling for quite some time.
I've seen several references to a "compact crankset" and questions like this one asking about replacing the whole crankset just to change gearing. Back in my day (get off my lawn you meddlin' kids!) I would have (and, occasionally did) simply changed a single chain ring to one with a more or fewer teeth to change the gearing.
Why would one now change the complete crankset instead of buying a single new chain ring? Does it bring specific advantages to the table, or are replacement/different size chain rings simply no longer manufactured? (The cynic in me says that means more profit for the manufacturers.)