I personally hate it when people just jam a whole nug in the bowl. It makes it harsher, it can often get hard to get a hit because too much or too little air gets through, and it can be a waste of herb. If you break up a dense little nug instead of smoking it whole it you will have more hits.
There are time when it has to be done quickly and without scissors. In that situation I still try to break it up as good as possible. It sucks breaking up nug without scissors sometimes though..... a fresh batch of good headys will almost always squish between your fingers.