Agile processes promote sustainable development. The sponsors, developers, and users should be able to maintain a constant pace indefinitely.
For most projects, the duration is measured in months or progresses endlessly. The team is always developing new features and expanding the product offering. In such environments, it is crucial that the team can maintain a healthy pace and never exhaust itself.
A long-running project is similar to a marathon; you can’t run full-out, or you’ll collapse and fail to finish. A marathon is not a series of sprints. Too many teams try to push extra hard every two weeks, with the last couple days having a bunch of stuff jammed in recklessly. Other teams have managers who crack the whip put the team on a death march for months at a time, to be followed by yet another death march.
These same managers also find it difficult to recruit great people and often have to deal with high turnover rates. Word gets around. There are many places to work in software development. People have a variety of options.
Another key factor in team longevity is the physical health of the team members. It is important for everyone to eat healthily, get some exercise, avoid illnesses, and reduce stress. Healthy developers will be more productive and will be able to put in more hours than those who are frequently exhausted or sick. Anything the team can do to promote a healthy lifestyle should be encouraged.