From MLB:
The catcher is not permitted to block the runner's path to the plate unless he is in possession of the ball, though blocking the path of the runner in a legitimate attempt to receive a throw is not considered a violation. The runner can be ruled safe if the umpire determines the catcher violated this rule. But per a September 2014 memorandum to the rule, the runner may still be called out if he was clearly beaten by the throw. Backstops are not subject to this rule on force plays.
When receiving a throw, catchers will often provide a sliding lane into home plate for the runner to lower the possibility that they will be called for violating the rule. Likewise, runners can lower their chances of being called for a violation by sliding in the given lane.
....clear as mud