There are a lot of configuration items that SharePoint cache by default: features, solutions and timer jobs among many other stuff. According to Joe Rodgers in this entry, “The config cache is where we cache configuration information (stored in the config database) on each server in the farm. Caching the data on each server prevents us from having to make SQL calls to pull this information from the configuration database. Sometime this data can become corrupted and needs to be cleared out and rebuilt.”. Yeah.
So just imagine, what could happen if you deploy a solution with a custom timer job, and you forgot in the first line of code something like
Boahhh: no trace, no error, no action, nothing.
Then you will probably need to clear the SharePoint configuration cache (like Joe Rodgers explain) or at least, if you know what is causing your problem, re-install the feature of your TimerJob. That will clear the cache for that feature/timerjob and when you upgrade your solution and install the feature again, SharePoint will cache the right one.