While I'm not asking the question "Why plan Web capacity?" to call this necessarily and useful question itself...
into question, it's a good idea to get back to basics of the discipline every now and then. In this case, my goal is to arm you with potential justifications for capacity planning should your upper management (or anybody else with decision making authority) raise that question to you in an entirely serious or straightforward way.
Indeed capacity planning takes time, and can often require purchase or use of expensive tools or modeling techniques. Thus, the question is worth asking, and equally worth answering. There are several primary reasons why capacity planning is entirely worthwhile, and why it doesn't have to produce hard and fast answers, either -- there are always ample opportunities to trade up-front expenses and investments against potential exposures or losses. The key is to help making such decisions voluntary and conscious, rather than involuntary and simply as a side-effect of other, more basic decisions.
Careful capacity planning can lead to some or all of the following outcomes:
Positive user experiences: As system loads increase, users can experience delays or, worse yet, may not even be able to access your servers. By planning for peak loads (and possibly even arranging for excess capacity when needed) you can plan for the most positive user experiences possible. If your Web site is a key ingredient for business or organizational success, providing positive experiences for all users becomes increasingly important. Proper capacity planning includes projecting peak loads, and formulating strategies to handle them, to help ensure that all user experiences are as positive as possible.
Maximize productivity: When system loads increase and response time, availability, and transaction processing capabilities suffer or worsen, your organization's ability to maximize productivity--or in more Web server-specific terms, to maximize the return on its investments in e-commerce, Web based information access, and so forth--will suffer. Proper capacity planning helps to ensure that productivity or ROI on Web investments can be maximized.
Avoid financial surprises: When peak loads force organizations into upgrading hardware, software, and/or service provider relationships, the costs associated with increasing capacity can be perceived as painful and unpleasant surprises. Capacity planning permits such upgrades and increases to be anticipated, planned, and budgeted in advance of their occurrence. In a manner of speaking, they allow you to pay now, and grow later, and to keep such growth under control.
Maintain stability and availability: By planning for peak loads (and monitoring and updating such plans on a regular basis) Web operators increase the odds of avoiding other unpleasant surprises that unplanned growth spurts can bring: slowdowns or outright losses of service. Capacity planning permits you to avoid such negative side effects, and to provide the best possible quality of service for your users and customers.
Arrange for emergency capacity: In those rare events when the best-laid capacity plans fail to predict real peaks (or when the direst disasters occur), proper capacity planning (not to mention business continuity planning) will allow you to arrange for either excess capacity (when unexpected peaks occur despite your planning efforts) or outright services replacement (when catastrophe strikes, or other forces shut your primary servers down) should they be needed. This is a case where cost-benefit analyses to compare the costs of purchasing such capacity against the benefits that such expenditures may or may not deliver are absolutely essential. But here again, proper planning can produce providential results.
Armed with these capacity planning justifications, you should be able to make a case for the time, effort, and costs involved in maintaining a well-crafted capacity plan, no matter what kind of managers or decision makers you must convince.
Ed Tittel presides over LANWrights, Inc., a company that specializes in Web markup languages and tools, with a decidedly Microsoft flavor. He is also a co-author of more than 100 books on a variety of topics, and a regular contributor to numerous TechTarget web sites.