The feature type may contain a lot of coordinates. Also, if it's not a really big data, the simple vector datasets we use in this recipe contain a large number of vertices:
gisdata=> select sum(ST_NPoints(geom)) from countries; sum -------- 548604
When you're creating a small-scale map, that is, a continent view, it does not make sense to have the GeoServer process all this data to output a really simplified rendering of the shapes. You are just wasting CPU time and degrading the performance of your server.
Having a simplified version of your data for general representation would be more practical, but you also want to have a detailed version of the data when your map goes to middle or large scale. ...