Ghost blocks appear when doing any form of insta mining. This ruins survival experience and plagues minecraft as mining is one of the main aspects of the game. The ghost blocks suffocate the player when they stand inside them, which once would have killed me if I didnt have a totem. Some could say that this is worse than block lag because you need to reload the chunk to find the ghost blocks

Ghost blocks can slow down 

-sand, terracotta, ice or any other type of insta mine resource gathering

-digging nether tunnels

-haste 2 eff 5 caving

-terraforming/landscaping

and probably more