That's right. You get to choose which clock source you get to use. The main reasons for one choice over another are:
cost: if you use an external crystal or ceramic resonator, then you have to buy that part and the cost might be $.50 or so. But if you can use the internal RC oscillator, there is no additional cost.
frequency stability: the accuracy of the oscillator frequency is the main thing that is different with the different oscillator choices. The most accurate oscillator is one using a crystal. The next most accurate would be a ceramic resonator. The least accurate would be either the internal RC oscillator or an external RC oscillator. For example, a crystal rated at 100ppm tolerance might be accurate to within 0.01% and then as temperature varies, you might get another 0.005% variation. To contrast, the RC oscillator is only accurate to about 3% and if you "calibrate" following data sheet descriptions, you might get down to 1% and then variation over temperature might still be in the 1 to 5% range. So crystal is much more accurate, but RC is cheaper. Most people use crystals. Ceramic resonators can also work and they fall in between crystal and RC for accuracy.