Traditional Planner during planning
- Considers that the developer works 8 hrs per day.
- Allocates tasks to the development team and allocates features to fit into 100% of resource budget available
- Takes Ideal Engineering Hours (IEH) into account. It could be anywhere between 6 - 61/2 hrs per day (from my personal experience)
- Allocates tasks only between 70-80% of the resource budget available. For ex: if there are 6 developers working on 2 weeks iteration. He would then plan for 70% of (6 * 10 d * 6 IEH). (ofcourse, keeping holidays, planned leaves into account)
I have created a rule of thumb, if the iteration length increases, then the buffer needed to handle uncertainty needs to be increased accordingly.
I have tried with 80% planning in a 2 week iteration period, and it worked well.
One of the columns in Product Backlog(PB), we have been using at Valtech is "MoSCoW rule". This rule is extensively used in DSDM community. This column is being used to prioritize the requirements. These rules are very handy and easy to understand, as comapred to "High, low, Medium" Or "1, 2 and 3" numbers. It is advisable to fill 70-80% of the PB with Must Have requirements, and the rest with Should/could have requirements. Customer needs to be made aware that, if new tasks get discovered during iteration, the 20-30% of lower priority(SCoW) would be dropped.
More info. on MoScoW rule is available here