18 May 2019

I often hear developers saying “I do XYZ because it saves my time”. “XYZ” could be the selection of programming language, the use of 3rd-party libraries or other choices in programming. When I hear this, my immediate reaction is always: where to put users’ time into the equation? Here is how I think about it.

In my view, the value of a feature is roughly measured by

value(feature) = #benefitedUsers * avgUserTimeSaved - devTime

It is a balance between users’ time and developers’ time. The feature is more valuable if it benefits more users and takes less time to implement. This simple “equation” can be applied to a variety of use cases:

  • In one extreme, I am the only benefited user for a one-off task. The user time is usually much less than dev time. The approach taking the least dev time is preferred.

  • In the other extreme, installation affects all users. For a tool with a large user base, it is worth every bit of effort to simplify installation, even at the cost of significant development time.

  • Most practical scenarios are something in between. It can be difficult to measure how many users may be benefited from a new feature. Experience in user interaction and familiarity with practical data analysis will play an important role in making the right decision.

  • A software project can be improved in multiple ways. Rationally, the most valuable feature should be prioritized.

  • Similarly, a developer or a team of developers may be working on multiple projects, it is preferred to work on the most valuable feature first.

Of course, in practice, the choice to implement a feature is more often opinionated than rational. There are also other factors into play. For example, if a developer gets paid to implement a feature (e.g. in case of LuaJIT), that feature is likely to get a higher priority.

The above measures the value of a feature from the developer point of view. From the user point of view, development time doesn’t matter. All users want is a product that is more convient for them. Next time when you argue development time is important, think about the potential users.

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