Hey Fappa!
Great question, I thought it might be a good idea to spell out some of the improvements that are a part of the Epic Story XP Boost. A lot of these changes can be found in the 3.2 patch notes which can be found here. Also, since I love bulleted lists, I am going to give you one those:
.The Epic Story XP Boost applies to the Class Missions of each class in the core game. In Rise of the Hutt Cartel it applies to the main story mission for each Faction.
.Each Class Mission now rewards far more Basic Commendations than before, which is a great way to stay geared as you level.
.There have been a ton of improvements to make travel easier (I will list them shortly).
Here are some of the relevant patch notes surrounding the Epic Story XP Boost:
.All Class Missions that previously rewarded 1 or 2 Basic Commendations now reward 8 Basic Commendations.
.The Planetary Modification and Equipment Vendors have gone through a large rework: The vendor's stocks have been adjusted to have a better variety of Modifications at a lower Commendation cost. In addition, the title of the NPCs has been changed to reflect the level of the items they sell.
.All Taxi Destinations are now available to all players.
.All Quick Travel Bind Points within a map region are now automatically discovered when the region is revealed.
.The cooldown on the Quick Travel ability has been reduced. For Subscribers and Preferred players the cooldown is now 6 minutes, and for Free-To-Play players the cooldown is now 26 minutes.
.The Legacy Travel I, II, and III unlocks now reduce the cooldown of the Quick Travel ability by 2 additional minutes each.
.The cooldown on the Emergency Fleet Pass ability has been reduced. For Subscribers and Preferred players the cooldown is now 90 minutes, and for Free-To-Play players the cooldown is now 180 minutes.
.The Legacy Fleet Pass I, II, and III unlocks now reduce the cooldown of the Emergency Fleet Pass ability by 30 additional minutes each.
.The base cooldown on the Priority Transport: Personal Starship Legacy Perk has been reduced to 6 minutes. Each Improved Priority Transport: Personal Starship unlock will reduce that cooldown by an additional 2 minutes.
As you can see, travel, especially with Legacy Perks is now much easier . I hope this wall of text makes the whole Epic Story XP Boost thing a bit simpler!