Slack Time
The best resource on the importance of “slack time” is Tom DeMarco‘s aptly titled book, “Slack: Getting Past Burnout, Busywork, and the Myth of Total Efficiency“. (I’ve loved everything Mr. DeMarco has produced since the 80’s.)
I’ve worked on projects where I had a lot of slack time available that allowed me to interlace learning with doing. I’ve also worked on projects where I was balls-to-the-wall; solely “doing” for the entire duration. While on the former, I felt grateful to be able to kill two birds with one stone. While on the latter, I felt angry at having no time for personal development.
Having too much slack time available on a project is certainly inefficient. It can lead to boredom and a guilty feeling of “not contributing” to the org. On the other hand, having no time to breathe can lead to unnecessary mistakes, corner-cutting, and an angry feeling of being exploited – especially if you perceive other teams as having too much slack time available.