Why Resources shouldn’t be assigned on a Summary Task

Resources should never be assigned on Summary Tasks as per the Best Scheduling Techniques in MS Project. It could leads to project corruptions (in few cases while publising), duplication of Work Hours when same resource is again assigned on sub-tasks, resource overallocation and mis-calculations of Work hours while honoring the dependencies.

Duplication of Work

1) Assigned resource “John” on Summary Task and again assigned him on another sub-task. Which will duplicate his Work hours. Look at the image below, Work rolls-up to 200 hrs.

2) Now I deleted “John” from Summary Task, which eliminated his Work from Summary Task by 9d X 8 hrs/d -> 72 hrs. So now total Work reduced by 72 hrs. to 128 hrs. Look at the image below.

Mis-calculation of Work hours to honor dependencies while a resource is assigned on a Summary Task

3) Resource “John” assigned on Summary Task and a sub-task below, Work hours roll-ups to 184 hrs. See the snapshot below.Refer to point 1 above it was 200 hrs. when all tasks were FS linked, but 184 hrs. when Task 2 and 4 are starting together. So, in this case due to different dependency type or absence of any link calculation is different than point 1.

4) Now after deleting John from Summary Task hrs. come to 128 hrs.So, if you refer to point 2 calculation remains intact.

If you would notice in Pic 1 and Pic 3 they are showing John as over-allocated which is due to duplication of efforts, which logically is not correct. In Pic 4 John is shown over-allocated which in fact is correct, as 2 tasks are starting in parallel.

So, to avoid all such mis-calculations and wrong estimations we should not assign resources on Summary tasks, even if it means that same resources are working on all sub-tasks, they should be assigned individually.