You can go too far, but the right add-ons can greatly increase a scattergun's capabilities.
You can put as much crap on your shotgun as you want. It's a free country. Some people go overboard, hooking everything they can to every Picatinny rail spot they can find.
There are a ton of aftermarket accessories out there, many of which can prove extremely useful and well worth the money. However, anyone can go too far when it comes to adding aftermarket products.
If you keep a solid equilibrium of weight, bulk and practicality, though, you can find that sweet spot between fun and effective.
On the cheaper end of the market, your common Mossberg 500 or Remington 870 shotguns come with a straight, traditional polymer shotgun stock. Some people prefer something a little more modern because they want a more personalized grip, or maybe they want the ability to add more attachments.
A common, inexpensive stock option is a pistol grip with an AR-style, telescoping, six-position buttstock, which can fit most lengths of pull. Some people don't like a pistol grip on a shotgun, though, as many feel it transfers too much recoil to their hand.
Fortunately, however, popular brands like Magpul make a wide variety of stocks that fit any of those common shotgun models. These stocks will often come with multiple sling swivel attachment options, from QD cups to old-school sling swivel studs. They will also typically include recoil pads, which can vary quite a bit in thickness and absorption.
Ammo: Capacity and Extra Shells
If you're setting up a shotgun for home defense, it's probably going to need a few more accessories. To be considered "tactical," a shotgun has to at least have an increased ammunition capacity over a hunting model, usually achieved by an extended magazine tube that's typically the same length as the barrel.
Even if a shotgun has an increased capacity, it's a good idea to keep a few spare rounds on board the gun itself. Some buttstocks have an optional shell carrier that can be mounted on the side opposite the shooter's cheek. A sidesaddle ammo carrier is also a popular way to carry extra shotgun shells.
They are typically polymer and mount to the receiver on the left side and hold six shotshells. There are also many slings with shell holders for 12-gauge or 20-gauge shells.
Gun Lights and Lasers
Even a double-barrel shotgun can benefit from a mounted light.
Most defensive encounters occur in low-light situations, and identifying your target is a top priority. Some shotgun forends will come with accessory rail segments or other ways of mounting a flashlight. These days, many include M-Lok rail system slots instead of rails, so the user can add just the rails they need.
If that's not an option, there are various accessories that clamp to the barrel or mag tube that allow you to mount a flashlight.
A lot of people elect to mount laser sights on their shotguns, as they not only work well, but they've also become very lightweight.
Optics and Choke Tubes
Many shotguns come with receivers already drilled and tapped for rail segments for the easy mounting of popular red-dot sights and other optics. These are excellent for close-range shooting and fast target acquisition, which means they're also great for home defense. Shotguns are quite forgiving when it comes to optics. If it can handle the recoil of the shotgun and hold zero, it should work just fine.
If your shotgun has a threaded barrel, it's worthwhile to get a nice set of choke tubes. These will allow you to fine-tune your shotgun patterns for various shooting distances and ammunition. And, with a more versatile gun, you can use it for hunting or skeet shooting without sacrificing your home defense firearm.