What are the technical reasons of updating SuperSU? After rooting a device , and installing SuperSU ( Chainfire or Coding Code Mobile Technology ) and everything is fine , let's say an update to SuperSU is  available say after a few months

Do I need to update ? What are the downsides , if any , if I don't ?

My understanding is that I don't need to but wanted to be sure with technical reasons / explanation . Googling didn't help.

Edit: This is not related to the problems with Ver 2.80 or 2.81 , this is a generic question

Edit 2: From Generic to specific - after reading changelogs, I don't understand whether I should Ver 2.79 to a later version on Moto X Play , 6.0. Can this be clarified ?
It is not necessary to update. But, it is always a good habit to keep your device up to date.

If you do not want to download so frequently, then see the change log of the updates, and decide whether you want to update or not.