Usually, it's a waste of time.
Internal developers generally earn per time-basis, so if the project takes one month or ten months, then they earn the same every month. Then, it's not rare to find that the performance of internal developers is low.
Also, it is not means quality, they surely have more time to develop, but mistakes still happen, and often. Even more, if the team of developers decided to adopt some new and shiny technology, then finally they found that they are working double, and they have a project developed with lots of moving parts.
Plus, internal projects, that is, projects made with the internal developers of a company, trends to change, and sometimes they are in constant changes. And a new change means a new deadline. Some projects that could be finished in 5 months could easily take two years.
Instead, usually, an external team (such as freelance) does not have such a way of work. Usually, they work per project and per deadlines.
IMHO, if we test 10% in unit-testing, then it is worth. Otherwise, it's a waste of time and resources. And some developers really love to spend time, such as updating libraries every day, doing a backup (that they should be done automatically), recompiling stuff and such.
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