It's always important to make sure you have the most up-to-date rules for your game. Something might've needed tweaking because it was unbalanced or the wording was ambiguous or whatever reason. Star Wars: Legion is the latest game to have an update. Fantasy Flight has posted one up, so if you've got an event coming up, or are just a hobby fan, you should make sure you've got the latest version of the rules.
From the post:
The latest version of the Star Wars™: Legion Rules Reference is now online! This update comes as players from around the globe are preparing for the World Championships at Adepticon 2020 from March 25-29 and contains the usual refinements and clarifications that come with a rules update. Learn more about these changes directly from developer Luke Eddy in the paragraphs below and download the new Rules Reference to see all the changes for yourself!