The MARSOC Raiders conduct missions that are slightly different from other units. Despite they are not designated as Tier 1 unit, they are still a significant fighting force in the U.S. Military arsenal.
Marine Corps Forces Special Operations Command is the most recent unit to join the Special Operations Command community. In my opinion, they are primarily a go-between the U.S. Army’s 75th Ranger Regiment and the Special Forces Groups (Green Berets). Their primary roles are for Direct Action, Special Reconnaissance, Foreign Internal Defense, Counter Insurgency/Terrorism, HVT hunts, and Maritime Interdiction operations.
The other thing that is important to note is that the biggest reason the Marine Corps was not a part of the SOCOM community is that the hierarchy within the Marine Corps didn’t believe that they needed to be as every Marine Corps unit is capable of being a highly effective DA, reconnaissance capable fighting force. The Marine Corps didn’t want those units being directed or commanded to do things that weren’t Marine Corps specific.
When the initial teams were stood up the Marine Corps drew from the Force Reconnaissance community almost exclusively so you got a special group of Marines who were the best in the business when it comes to Reconnaissance and DA skills that rival the SEALS. Initially, there was a huge push back by other units within SOCOM specifically Green Berets who felt the Raiders were invading their exclusive domain. It’s said the commanding general of the JFK Special Warfare School told the first Marines to go through the Q Course that he would rather burn his Beret and Tab then ever let a Marine earn either. Now they recruit from across the Marine Corps and they aren’t quite the red-headed stepchildren.
Since 2006 the Raider Regiment had built a reputation worthy of their lineage. They had bumps along the way but most Special Operations units do in their infancy. Since then they have been deployed around the world and have been conducting missions we will never hear or learn about. In Afghanistan, they were in my time there conducting mostly DA missions, almost 90 percent of the total in-country, and Counter-Insurgency roles. I would recommend reading Michael Golembesky’s books about a MARSOC team in Bala Murghab for a better description.
But to answer the question. Raiders don’t do anything that isn’t replicated by another SOCOM unit. However, by this redundancy it allows somewhere around 1500 operators to conduct missions that might not have been done or allow Ranger, Green Beret, Delta Force, or SEAL teams to have a longer downtime between deployments because they can operate instead.