He is talking about how if you use winrar free version you always get a popup asking you to pay.

However this really only mattered when rar was actually a good compression format. Today 7z has better compression and is used, not to mention your 7zip application can also do .rar

Which reminds me I need to reprogram my .bz2 thing I use to compress the servers maps to use the 7zip version of bz2 which is multi threaded so save time.