One additional consideration if you track actual time through timesheet entry in project.
When a resource is assigned to a summary task, that summary task will NOT appear on the resources timesheet since Project only shows the detailed level tasks. That’s part one of the issue.
The second part of the issue is that Project will “make up” timesheet hours for resources assigned to the summary task. Meaning not hours ever reported by resources. For example, if Bob is assigned to a summary task for 100 hours and there are a bunch of detailed tasks below it that resources are in process, with those resources entering actual work hours thru timesheet data. If the sum of all detailed tasks indicate that the entire block of tasks (under the summary) is 75% complete, then Project will magically add 75 hours to Bob, even if he didn’t work those hours. Why? because if all the detailed tasks are 75% complete, then Bobs work must also be 75% complete and Project will adjust Bob’s actual work hours to make that formula true. So it will give Bob 75 more hours of actual work.
Bob may have worked 40 hours that week on other detailed tasks, but because of this quirk, Bob could end up with hundreds of actual hours being reported that week depending on how many summary tasks he is on.
Bottom line, if you are using timesheets to track hours to accurately report project hours and costs, do not assign resources to summary tasks.