Summary: 
There is no way to differentiate comments that are entered by an employee when submitting a timeoff request and, comments entered in the timesheets. We run reports where we want the comments to be included but only the comments from the timesheet. We do not want the comments included on these reports that employees write on their leave requests that explain why they are requesting and using leave.

Resolution:
To archive this requirement, create a custom column by name Time Comments and insert the following condition into it.

If(TimeOffHours>0,"",Comments)

Enable this custom column and disable the standard Comments column in the General section under report Settings. This essentially says if there are time off hours on this report line, do not display anything, otherwise display comments.