Jerk With a Heart of Jerk

The idea of a jerk with a heart of gold-- someone who, for whatever reason, hides their kindness behind a unpersonable facade-- is so well-worn in fiction that readers start looking for it the moment a grouch shows up on the scene.
This is probably the reason I like fictional jerks who are unrepentant about their selfish ways. Bluntly, it's refreshing.
The other reason these characters can be a positive influence on your writing-- albeit in controlled dosages-- is that it's tempting to write characters who are good to the point of irritating the reader. A genuinely selfish character, on the other hand, can immediately add friction to the story even when they're behaving in a socially acceptable manner. After all, the reader will immediately be suspicious of their good behaviour, and start looking for schemes and hidden motives, which will almost certainly exist.
Having a character with strong motivation, even if that motivation isn't the most appealing, is an important plot driver. And sometimes a jerk can do wonders for your plot. They can be a wild card in some respects, as they are likely to place their own short-term gains over the good of the group, whether that's ratting out the bad guys to get a reward, or turning in the heroes for some petty revenge.
These characters are also uniquely positioned to be chronic do-gooders who don't annoy the reader. If someone saves the day to save their own behind, or because it's their job, this can be much more appealing than a saccharine cutout who works at their charity job saving inner-city kids, and then goes home to train orphaned sloths as guide-animals for the blind. That level of selflessness not only strains suspension of disbelief, but can be incredibly boring; a firefighter who rescues people from burning buildings because they like the attention and accolades is interesting.