In computing, as in life, taking the time to fully understand what you are trying to accomplish is never a waste of time. Sun Tzu clearly knew a great deal about computer hardware and software when he gave us “故曰：知彼知己，百戰不殆；不知彼而知己，一勝一負；不知彼，不知己，每戰必殆.” If you know what you are trying to accomplish and you know what the hardware is capable of then you cannot lose. If you know one and not the other you might as well be flipping a coin. An absence of knowledge of both will certainly lead to a poorly running computer and or inefficiency in cost.
A case in point is a computer used in a family or office setting that will never play games. For this application, modern CPU’s are way beyond the point of being “fast enough” even on the extremely low end. Even going as low as $47 won’t make a difference. Web browsers and office documents are going to so very rarely be CPU bound spending more is going to get you very little in terms of actual performance payoff. Even more inefficient would be spending to the point where you are adding cores. Slotting a quad core into a use-case like this will result in nothing more than double the number of idle cores sitting around twiddling their expensive thumbs all day. Web browsers like Chrome can thread out very well, but we have to be keep in mind that your typical office worker isn’t going to be using the browser in such a way that it can cap out a cheapo dual core. I doubt Joe in Accounting is going to be pulling up 100 tabs of flash based streaming porn. And if he does, that’s more of a management problem than a computing one.
Your time spent understanding the use-case extends perhaps most importantly to storage. Hard drives are going to be the least expensive still. Analyze how much space your users are using currently. Most will likely never have any case to store more than 128GB locally. If you are a large enough business, allowing anyone to store things locally is a bad idea anyway as that creates a single point of failure for data that could very well be of critical importance to your operations. This problem is best handled with a GPO and an Active Directory member server running RAID. Also with storage it’s worth considering if the slight cost increase of going to an SSD is going to payoff. I think in most cases it will for this type of work if we consider how expensive labor is. The combined cost of 20 workers waiting for their computers to boot up or lagging behind as the storage catches up with them is going to cover that initial cost outlay very quickly. Consider the cost delta between a decent spinning disk and a good quality SSD. Even if you somehow pay minimum wage it will still payoff quickly. Other things are less quantifiable such as the reduced stress of having your workers using fast storage. If they are anything like me I know I get frustrated when I have to wait for things to load.
Another thing to consider is size. Since our office and web browsing machines are so low power they don’t need to be very large at all. Machines running our very cheap Intel CPUs and solid state storage should only be able to peg maybe 50 watts of power at full tilt. They will spend 95% of their lives using half that. You can easily get by with using a form factor such as mini-ITX. This will use up much less desk space and, rather informally, look bomb. One I built recently for such a purpose is roughly the size of your typical George R.R. Martin hardcover.
This cute little guy is purpose built, dirt cheap, and boots and opens programs with enough speed to really blow your hair back.