For other kinds of jobs, allowing concurrent executions of multiple builds may be problematic, for example if it assumes a monopoly on a certain resource, like database, or for jobs where you use Hudson as a cron replacement.
If you use a custom workspace and enable this option, all your builds will run on the same workspace, thus unless a care is taken by your side, it'll likely to collide with each other. Otherwise, even when they are run on the same node, Hudson will use different workspaces to keep them isolated.
It's possible to use Job cascading feature for this property. Please review this document.