Combat Movement

Combat in D&D is supposed to be simultaneous, but is governed by the use of rounds to make the game playable (PHB 189). The RAW allows Movement to be broken up between or during other actions (PHB190). This is bad:

• It allows low-risk ranged attacks (spell or normal) where a caster/shooter can stay behind cover, step out to shoot and duck back into cover. Enemies that wish to respond must Ready an attack but since Readying allows no Move when an attack is made, it means that anyone trying to deal with a sniper using this "move-shoot-hide" approach must remain in the open at all times
• Moving between attacks (melee or ranged) implies that the enemies are static. However, the simultaneous nature of combat means the enemies are assumed to be moving all the time
• Remaining 'Partial Movement' must be tracked, which adds to combat book keeping and slows things down.

To address these issues, Movement cannot be broken by an action and then resumed. Any movement not used once the actors Action is activated is lost. Note that some spells or class abilities grant the character extra actions which may be used for movement. These abilities are not impacted by this change. When in doubt, think about it this way: once the character has started a move, he may move until out of movement or he decides to do something else. As soon as the decision to stop is made, that Move action is over and some other action can begin.