A combo amplifier combines both the head (the power source) and cabinet (the speakers) into one unit that can be transported as a single piece. It's ideal if you plan on playing small gigs where lugging around heavy equipment isn't practical or want something portable to travel with. A head and cabinet system allows you to mix and match different cabinets and heads to get the perfect sound for your setup. You can also upgrade your amp down the line by changing out just the head or cabinet.