Cost:
Airguns are generally cheaper to buy and for sure cheaper to shoot. Airguns can cost as little as $50-100 to buy while real guns in similar models will cost many time more. Cost of ammo is so much less expensive than Real Gun ammo by a mile!
Difficulty to Obtain:
Airguns in most countries do not require any licensing or registration. Generally there are more available options in Airgun choices than Real Gun choices as restrictions often prohibit many Real Guns to be obtained.
Places to Shoot:
Unless you live in a super remote locations and your laws allow you to shoot Real Guns in those locations, then in most cases you can shoot an Airgun almost anywhere within reason. You can even shoot certain Airgun models in your basement. Airsoft is a great option for indoor shooting as the plastic ammo does not carry very much energy so with minimal effort you can make a backstop that will trap the ammo very well.
Trigger Time:
Because ammo is much less expensive and places you can shoot are easier to find, you can get a lot more Trigger Time under your belt which will also improve your shotgun with Real Guns and after all it’s just fun to shoot guns even if they are Airguns.
Safety:
I am not talking about safety in terms of protection. I am talking about safety as in if you do something stupid and your Gun goes off accidentally. If you accidentally fire your Airgun indoors, the bullet will not travel through floors or walls and potentially harm or kill someone on the other side. If you do manage to shoot yourself with an Airgun, the consequence are much less severe than shooting yourself with a Real Gun. That said, always treat an Airgun as if it was a Real Loaded Gun, as server injury and even death can occur even with an Airgun.
Ware Games and Training Situations:
There is no way you can use a standard Real Gun to shoot at people, unless extensively altered with special parts that make the Real Gun unusable to shoot live ammo. With Airguns you have the choice of using an Airsoft or Paintball gun that are both designed specifically for this purpose.
Pest Control:
If you have the need for pest control in an urban area where you do not want a stray bullet to travel too far or penetrate buildings if a shot where to go awry, then an Airgun designed for accuracy and power may be perfect for the job. Accuracy with target and hunting Airguns is on par if not better than many Real Guns and are have powerful enough to kill a pest humanely without having too much power for the job and having to worry as much about your background.
Prop Guns:
As mentioned already, Airguns can look a lot like Real Guns, so they are perfect to be used as a stand-in or Prop Gun when you need to simulate the look and function of a Real Gun. Again they are easier and cheaper to obtain and if something does go wrong, the consequences are much less severe.
Social Stigma:
Unfortunately Real Guns and perhaps any gun these days are looked upon with a social stigma as being the cause of the Crime rather than a tool used in a Crime. And so people blame Guns for these crimes rather than the people committing these crimes. If a person is motivated enough to do something bad, they are going to do it either way and will use whatever means is available to them to commit these Crimes. Including other means like: Knives, Blunt Objects, Poisons, Vehicles, Explosives… Sad but true! Airguns are not used in homicides or mass shootings as they are completely underpowered for a crime like this. They can however be used in crimes as a show of threat, as they do look a lot like real guns, generally people that use Airguns for real crimes, if challenged will give up immediately as they are completely outgunned. Don’t bring an Airgun to a Real Gun fight, you have better chance with a knife!