Understanding where your rounds will impact influences how you use a red dot at close range.
Being able to correctly adjust your point of aim is important to know to properly raise your point of impact. This can be crucial if you are trying to hit a certain place when dealing with a threat and you are not able to transition weapons systems to you pistol quick enough.
In this video from the National Shooting Sports Foundation (NSSF), Adam Painchaud of the Sig Sauer Academy shares a rifle drill that can help improve your accuracy on precision shots at varying distances. Adam demonstrates this concept with an AR-15 but this concept is applicable to any modern sporting rifle (MSR) setup with red dot optics.
Pretty easy and straight forward. By understanding the concepts of holdover and offset, you will be able to use your AR and Red Dot effectively together at any range that you need to to defend yourself.