Why would WAAS allow compression for content that rarely changes? Wouldn't it make more sense to suppress-compression for that content, take advantage of DRE and WAAS ability to cache that content for branch site browsers to consume? Is there a reason to allow server compression for static content?
Taken from 4.2.1 release notes
Step 11 Check the Suppress server compression check box to configure the WAE to suppress server compression between the client and the server. The default setting is unchecked.
By checking this box, you are telling the WAE to remove the Accept-Encoding value from HTTP request headers, preventing the web server from compressing HTTP data that it sends to the client. This allows the WAE to apply its own compression to the HTTP data, typically resulting in much better compression than the web server for most files. For some file types that rarely change, such as .css and .js files, this setting is ignored and web server compression is allowed.