<p>I think I might be missing the point of having a logging framework for your application.  In all the small apps I've always written a small "Logging" class and just pass log messages to a method in it which is written to a file.  </p>

<p>What is the purpose of a 3rd party logging framework like log4net?  Is it thread safety with logging write operations or am I missing something?</p>

you might want to switch to log to a db for some message, or an alerting system that pages the poor person on support
More importantly though, most logging frameworks allow you to specify the loglevel of different classes so you dont need to cut a new binary each time you want more/less logging (that verbose logging for the bug you just spotted in production)
Log4Net's site
has more detail