Perhaps you could have a look at Tavmjong Bah manual. That will show you which ones are best suited for vector objects or for bitmaps or sometimes with the two.
However this is also important to test some objects with somewhat dull colors or colors slightly fading to black or white.
If you are interested the default vector objects I use for testing are here on OpenClipart :
http://www.openclipart.org/detail/26679Take care also there are two kind of combining filters together :
1° apply a filter and apply a second one or more directly afterwards ; this is the default Inkscape behaviour and it is usefull to build new filters, but as that will combine them into a complex and heavy filter and the results could be unexpected ;
2° apply a filter, then do Ctrl+G before applying a second one and each time before you want apply any more filter ; this is the best solution to overlay them while keeping them separated in the file and in the Filters Editor.
ivan