Using a pocket holster has multiple benefits. The first is, yeah, covering the trigger. That's just gun safety 101.Why would you want a trigger guard for that model? You don't have to worry about accidentally pulling the trigger, unless you panic and squeeze too hard while pulling it out from your pocket. It doesn't have a safety because the trigger action is like an old, hammerless .38, with a long pull and substantial pressure.
Secondly, a proper pocket holster keeps the gun ORIENTED correctly (grip-up). A loose gun can rotate, and when you go to draw, you may get a handful of barrel or receiver instead of the grip.
Finally... as has been mentioned already.... When you pocket carry, NOTHING else goes in that pocket.
Thirdly, an unholstered gun in a pocket prints BADLY. A pocket holster prevents that printing.
I pocket carry a S&W 642 Airweight, which is "hammerless" (hammer is not visible externally) and has a fairly heavy trigger. I wouldn't dare carry it without a proper pocket holster.
Edit to add: I just saw that LabGuy just posted the same thing, pretty much!