There are a few key differences between the two. A USB-C to USB-A cable has a rectangular connector on side with 4- to 9-pins in it. As you know from trying to plug a mouse into your PC, it only fits in one way and you usually never get it right the first time.
On the other end of a USB-C to USB-A cable, you will find the modern oval USB-C connector, which fits in both ways and packs far more pins and wires inside. The short story is that a Type A to Type C cable will typically charge at much slower speeds than a Type C to Type C cable as well as transfer data at far lower data rates.
That isn’t always the case as some phones that use special Type A to Type C chargers and cables will indeed charge very fast—but they’re usually proprietary. With most new phone chargers going to USB Type C, you’re probably going to usually want a Type C to Type C cable.