Make sure that you are the latest patch level of Sybase to use MTB feature.
You can isolate logins based on applications, or access privileges, or even resource consumption. Always reserve a tempdb for a sso/sa priveled account.
This also slightly increases your recovery period whenever you recycle your dataserver. So, keep the MTB's to the lowest size that you can afford.
The login bindings are stored in master..sysattributes, take a nightly backup of sysattributes, so this can be restored in the event of an failure.