+1 to the above. With my work/family schedule it's not uncommon for a beer to sit in primary for 3 weeks. It's not needed necessarily, but all I know is my beers never, ever have diacetyl, acetaldehyde, etc. So the yeast are getting ample time to clean up and drop out (most strains) before I keg. As for dry hopping an extra couple days past 3 days, no worries.