First, so you know, I also own another Benelli M4 with the full 18.5" barrel that I am waiting on some 922r parts and a 7rnd Mag tube.
Long guns and houses don't go together super well for maneuverability, also the longer it is, the better leverage the criminal has on wrestle it from you, Also will start to spread a bit sooner than the longer barrel will. If I need more than 5/6 slugs or buckshot, I should have practiced more or grabbed an AR for defence. Most my rifles and shotguns get shortened with Form-1, where I live even when hunting there in NO way you can shoot past 100yds because how thick the forests are, and even 10" barreled rifles can drop game at that range. Plus on my rifles, all the barrel I don't have range to benefit from, I can put on a suppressor and it not be horribly long overall.
Then there is the whole cool factor thing. They make bigger fireballs, bangs, usually look cooler, draw in more convo at the range, etc.