An additional advantage (sometimes disadvantage if you are not a M$ user)is that you often recieve an OEM pricing for the OS which can be a substantial savings over buying a retail boxed OS package. Also, be aware that there are sometimes integration issues when you buy pieces to build a system. The box dealer has usually worked out these problems prior to selling you the complete system. What it comes down to is how much of the process you are wanting to do and how much hassle you want to put up with when there are problems.