Gotto wonder if people that don't mulch their pots outdoors have a functioning brain in their head ? It plays a couple of very important roles in the nutrient cycling process so is twice as important for anyone running (or think they are running) an organic system,without it your top layer of soil which should be your most active becomes an unproductive dead zone. There's plenty of different types of mulch that can be used even a thick layer of compost will work effectively, I usually start with lucerne chaff that I shred up in a barrel with a brushcutter so it breaks down faster then later on in the season after I've built up the top layers via top dressing over the previous mulch layer a few times I'll use sugar cane mulch as a final layer.
This is what I like to see when you lift up the mulch,fungal mycelium networks drive nutrient cycling more than any other microbe.