How much does developement time matter?

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.