Plugging rear ports of "bookshelf" speakers?

I did a search here on A'gon to try to find out what the reason for this would be, and I take it to tame unruly bass?  Would plugging the rear ports make a speaker less particular about placement?  I would think that if anything, plugging the rear ports would mean the speaker could be moved closer to the wall, but I find that I am often mistaken about my preconceived notions.