When to use Timer Jobs and when to use Windows TaskScheduler ?

Hello,

I have few general Question ..

1. What is Timer Job and in what scenario we should go with TimerJob ? Any example ..

2. What is windows TaskScheduler and  in what scenario we should go with TaskScheduler  ? Any example ..

3. On which credentials SharePoint list Workflow runs ? System Account or Current User who created the workflow.?

4. Why we should create SharePoint 2010 workflow using SPD 2013 ? Is it advisable if yes than Why ?

Thanks,