There are 2stage in reloaading a firearm
1st insert the megazine
2nd pull the charging handle
In current version if reload process gets disrupt somehow after inserting megazine,then everytime we have to start the reloading process again from the beginning.
In stage reloading feature if you complete the 1st stage of inserting megazine and reload gets disrupt then while reloading again it will continue from the 2nd stage of pulling the charging handle. Reload process won’t reset everytime.