I've now observed a few development teams using Trello to manage their work. Trello feels great to use and it seems to promote creativity and participation, which is also great. There's some things it doesn't help as much, where personal discipline needs to be brought in and used consistently, if the team is to stay focused and continue making good prioritization decisions.
Making estimates. While it's possible to install an extension to Trello to get estimates on development cards, it is not built in throughout the system. Personally, I never get involved in development work without estimating my tasks; I want the product owner people I work with to value my time. Estimates help them do so, and estimates also clarify conversations over features that have unnoticed ambiguity. Estimates are a critical communication tool for me.
Tracking velocity and releases. Velocity helps teams predict and keep focused. If we'd like to release a beta in 4 weeks and our velocity is 12, and we have a lot of tickets estimated at 1, 2 and 3, one quickly sees how they add up to 2 weeks or 4 or 6. It's good to have the velocity and the estimates very well tracked and lined up against desired milestones. We all need help making sure things don't creep into the next four weeks unless they are really required to release the beta. With Trello, tracking velocity and comparing it to release dates needs to be done outside the tool.
Keeping focus on epics. With agile development, it's easy to get distracted from an epic -- a larger feature that requires a bunch of things to come together before it can be released and useful. Small things come up and because they're small, the team may be attracted to just finishing those things off. How can you keep noticing when a task doesn't help meet an Epic goal? With Trello, it requires unusual discipline to keep a list of Epics cards sorted and make sure that every development card is tagged with the appropriate epic.
Have I missed some critical features of Trello or patterns of use that would achieve these goals? I would be happy to learn I had, because it would allow me to advise teams using Trello currently.
Personally, I like it when tools help provide discipline. I'm willing to live with less flexibility in return for help keeping disciplined. It's easier for a whole team to adapt to the discipline of a tool, than to have the project manager or other disciplined person always nagging the team to add the right label, to put in the estimate even though the software doesn't require it. My opinion isn't universal, but it is mine, and for those reasons I prefer Pivotal Tracker, or in a pinch I'll even use Jira/Greenhopper over Trello.
