The Fitter is typically run multiple times and uses the best result among them.
If you check this setting, the next time you run the Fitter, placement and routing for the placement condition of the value displayed in the Seed: column will be executed only once.

This is a useful feature for evaluating "what results can I get with this seed value?" when the Fitter is complete but performance is not achieved.

* Depending on the design, it may not be very effective.
* A timing error may occur during timing verification.