Hi Kannan
1. The Scenario 1 & 2 is common popup message either when same user ids are logon to multiple times in different terminals. Or same user id log on different terminal "Select the option terminate other log on"
2. Why you want to keep the common user id? When you want to do troubleshoot in that time it’s very difficult to find the right user id and terminal name.
3. If your falls on performance issue you have to check those transactions enabling the ABAP trace, by using the transaction code ST12 trace. Check the overall ABAP & DB usage
BR
SS