It would be really cool if one could establish predecessor relationships between tasks. Frequently one task can't be worked on, or at least completed, without another one being completed first. Having that information visible is useful in planning. Furthermore, if I have a finish-to-start relationship between two tasks to be completed on the same date, it helps if you could configure Doit.im to not show the dependent task, until the predecessor is completed. This helps focus.
To sum it up, having predecessor relationships helps planning, and afterwards - while working - helps focus.