You can purchase and implement the oscillator component and know that the frequency output will not likely change due to conditions on your PC board provided you supply a good power bus and keep the temperature within working range.

Another advantage of the oscillator is that these units are typically able to drive a good sized load without additional buffering.

Still another advantage is that the metal package of some parts makes the operating frequency much less sensitive to stray electro/magnetic fields.

Sometimes boards will need several several different frequency sources and the use of shielded can type oscillators will keep one source from pulling the other off frequency. Crystal circuits on poorly designed boards can have this problem if there are long traces between the crystals and the active circuitry that makes up the amplifier circuits.

Hope that helps out.
Michael Karas