For some of our tasks, we don't work continuously on them, but we still need a start and an end date. For instance: write that White paper, will take you two weeks of discontinuous work. But you still know when you need to start that task, and you also know its due date.
At the moment, using start and end date fills our planning with big time blocks that lets you think that you can't do anything else in the meantime.
Using Start & End Markers (flags), linked by dashes for instance, would make it clearer. We already have the Milestone flag in Wrike when assigning a date, that would be little effort to add this possibility I think.