I'm not sure where you got that definition of Total Slack. Total slack is the difference between late start and start or late finish and finish. From help:

The Total Slack field contains the time a task's finish date can be delayed without delaying the project's finish date.

If a task's only successor is SS then delays to the end of the task have no effect unless the finish of the predecessor task goes past the successor. However, the task may very well have zero total slack because any change to its start will change the successor start.

ok so if the only successor is SS, then the total slack definition is not true isnt it? so in other words, for a proper schedule to exist, we must always tie the finish of each activity to something

No, I wouldn't say total slack definition is not true if you have SS links. I would say that start to start links mean that the finish of the task in question has no impact on the end date of the project, unless the finish extends past the latest date.

You need to review the logic in your project and determine what are the correct link types for each relationship. Tasks without successor or tasks with only a SS link imply that the finish of that task will not affect any other task in the project.