When you create a segment, you choose whether the tasks it contains will be performed in order (sequentially) or simultaneously (in parallel). Your choice determines how the segment's duration is calculated. A segment's duration is used to determine overall deployment progress. If you select parallel, all tasks are assumed to start when the segment starts, and the duration of the segment is equal to the length of the longest task. If you select sequential, tasks are also assumed to start when the segment starts (unless you select the Sequential Execution Enforced option), but segment duration is calculated by adding together the times for all tasks. Finally, if you choose Sequential along with the Sequential Execution Enforced option, only the first task starts when the segment starts, and all tasks must be performed in order.