A pocket holster has two primary functions. If it cannot do those things, it's not worth having, and pocket carry without one is foolhardy. 

A pocket holster keeps the trigger guard protected, and allows the gun to be drawn clean from the pocket or at least helps. 

If you're going to pocket carry, either as a primary or supplementary carry method, let's go over what you should know about pocket holsters. 

At its core, a pocket holster is about practicality and safety.

The most important job of one is to protect the trigger guard, which is the job of any holster. Accidental discharges are a real risk with a pistol carried in a pocket without one, regardless of what type it is. ADs have absolutely occurred with snubby revolvers just as much as they have with striker-fired micro pistols. 

It keeps your firearm positioned correctly in your pocket, ensuring that it doesn't twist or turn. This aspect is crucial; if your gun isn't oriented properly, drawing it in a tense situation could take longer, be more complicated, or possibly lead to an unintentional discharge.

Additionally, a pocket holster helps conceal your gun, preventing it from printing - an outline of your firearm showing through your clothes. With an effective pocket holster, even the most observant person will find it hard to tell you're carrying. It also protects your firearm from lint, dust, and other debris, keeping it clean and ready for use when you need it the most.

But the pocket holster and pistol have to be paired with the right pair of pants, specifically in terms of pocket space. The roomier the pockets, the easier it is to conceal a holster and handgun in your pocket. You should be able to put your hand in the pocket and have the rim of the pocket go all the way up to the wrist. 

If you're going to pocket carry, pistol selection does and will matter. Larger, bulkier models just won't fit comfortably or discreetly in a pocket. For pocket carry to be effective, you'll want to consider compact firearms. 

The classic pocket pistol is a snubnose revolver, as 2-inch S&W J frames and Colt D frames (Cobra, Detective Special) were more or less the default for most of the 20th century. 

However, sub-caliber micro semi-autos in .380, .32, and .25 ACP were also very popular choices. The Colt Model 1908 Vest Pocket was literally named for how people carried such pistols. And there have been a great many other guns made with a similar form factor made over the entire 20th century and into today. 

What you're looking for is a slim, compact, lightweight gun that's small enough to fit in the pocket with the pocket holster. Modern subcompact single-stacks are about the upper limit of what size of gun you can successfully carry, though some of the subcompact double stacks like the Sig P365 and Springfield Hellcat could be pocket carried given their lightweight dimensions. 

With that said, once you've obtained a proper pocket holster, paired it with the right choice of firearm and wardrobe that will accommodate it, pocket carry is a viable concealed carry method either as a primary or supplemental carry method or for a backup gun.