Everyone has an opinion, some for a sling some against a sling, and the reasons are as varied as the people themselves are. There are legitimate reasons for having a sling attached and there are some legitimate reasons not to have one attached to your home defense firearm.
Obviously, a sling is used to shoulder a long gun so you do not have to bear the weight with your arms, and this is particularly important when out hunting, or hiking with a weapon. You would have to shoulder your weapon when stepping over fences if you are alone and cannot hand it off or when climbing a tree stand and so on.
For home defense, carrying your long gun for several hours is not an issue but being able to shoulder the weapon to transition to a handgun is important. Weapon retention is critical. If you fire your shotgun or rifle empty, you cannot just throw it down, you would have to shoulder it, and reach for your pistol.
Will you be in a situation where you empty your shotgun and still need more firepower? Not likely but you do need that option, because the shotgun/rifle could jam or otherwise malfunction.
You hear a noise you grab your shotgun or rifle, and head for your children’s bedroom. You need to get them under the bed or to the safe room, and you do not have a sling, what do you do? Your spouse/partner or some other family member needs help getting up, help through a window or simply needs help walking and you do not have a sling, what do you do?
A sling could catch on a doorknob or the corner of a counter top or chair back. However, is the fear of this enough to do away with a sling altogether. Is it realistic to think that your sling if properly adjusted will be dragging and snagging on everything. Practice drills will tell you whether this will be a problem or not. You will not know until you do some dry runs and create all possible scenarios or as many as possible anyway, because no one can predict what might happen.
Noise discipline, will your sling rattle, or slap giving away your position. Not likely unless it malfunctions, or is installed wrong or otherwise is not operating correctly. Swivel slings give you mobility without creating noise.
Can an aggressor grab the sling and get control of the weapon. If someone is close enough to grab the sling, then that person can grab the barrel or other parts of the weapon to gain control.
Can a shooter’s hands become tangled up in the sling, or will a sling otherwise interfere with their shooting? It could if the shooter is inexperienced and the sling is not properly adjusted or malfunctions and breaks loose. The possibilities would be endless and you could play the “what if” game forever.
Whether to have a sling or not on your home defense weapon may come down to personal preference, skill and confidence. Essentially, it is whatever you are used to, and what your comfort level may be. If you are convinced, a sling is a hindrance then it will probably end up being a hindrance.
If you are not convinced either way, then practice with one and without one. There are various types of slings that allow the shooter various carry methods and in some cases, a weapon can be engaged when it is shouldered with certain slings.
Practice, practice and then practice some more.