Timer Jobs
Timer Jobs are very important thing in SharePoint 2010. Timer Jobs are workhorses of SharePoint. Timer Jobs are nothing but a defined XML file which is stored in Configuration database which are executed by Windows Service - "SharePoint Timer".In SharePoint 2010, the Timer Job is linked under the Monitoring section in Central Administration.
SharePoint 2010 introduces the capabilities to assign a preferred server for running a timer job against specific configuration database.
Whenever you want to deploy your timer job into WebApplication scope, you will get an "Assembly cannot be loaded" loaded exception. This is because of whenever you are trying to deploy a timer, the timer will search for the DLLs from the GAC and not from the Bin of the Web Application.
Hence, always, the timer job should be deployed on the GlobalAssemblyCache.