The main difference is that porcelain is always waterproof whether or not it's glazed.
Sand and, sometimes, glass, is added so it is heavier, making it ideal for heavily trafficked areas. These can also be installed as tub and shower surrounds or used outside on decks, patios, and pool surrounds.
The color of porcelain is always milky white, but it can be made to resemble almost anything from leather to wood to natural stone.
Nothing gives a home so much architectural and design interest as marble, quartz, slate, limestone or travertine, but it's expensive when pulled directly from the quarry. It's also challenging, what with the porosity and softness properties.
Porcelain tile, designed to resemble stone, is a good, budget-friendly alternative.