link: https://forum.overdosed.net/topic/67547-desynchronization-desyncsynchclagsink-how-it-works-how-to-do-it/
Desynchronization, or Desync (Sometimes called Synch or Clag or Sink as well) is when a character creates server latency due to a run/walk speed discrepancy in server communication. Or in Layman's Terms, when someone is Desynching, they appear on everyone else's screens in a different spot than they really are. How "long" the desync is (The distance between where they're projected to be and where they're really at) is determined by how much Faster Run/Walk is granted by skills and charms, versus how much speed is granted by gear. Faster Run/Walk from gear does not add to Desync and could actually lessen the desync length by reducing the discrepancy. This happens because the game fails to take charm and skill speed into consideration when sending information to the server. So it shows the character where it would be at if it did not have that extra speed.
~Let's break it down
For the purpose of the analogy, let's say that Diablo 2 was turn based and characters moved by tiles.
Let's also say that each 10% Faster Run/Walk (FRW) equates to one "tile".
-If a characters gear has 20% FRW, it moves 3 tiles in a turn.
-Let's say that 10% of that FRW is from charms and 10% is from gear. There is a 1-tile discrepancy.
-In 3 turns, it would move 9 tiles.
-However, on the opponents side, it would show you where you were at after you had moved only 6 tiles.
-This means that you could be in their face and they don't even know it yet, because the server is showing them at tile 6 instead of tile 9.
I can no longer find the source that said so, however, I do recall reading that desync has a limit, as the server supposedly resets all locations every 15 seconds. This means that there's no guarantee that your character will desync very far.
Hammerdins are the most obvious and prevalent case of desync (At least ones that choose not to just tele-spam), as the build maxes Vigor and uses it in combination with Charge. This creates desync latency easier and faster than any other build. However, any character with a lot of speed from skills and charms like Wolfbarbs or Frenzy barbs can also desync very well.
I once had a level 30 Frenzy barb (Name Supafly taken after expiring) that had all 10Max/10-20AR/7%FRW GC's. Believe it or not, he was actually most effective at killing Necros than any other build. In LLD, one of the Necros biggest strengths is Bone Prison. However, against a Frenzy barb like mine, it was a liability. This is for multiple reasons, but extreme desync from a fully-charged Frenzy was a huge factor. Necros would just get steamrolled and mostly because of Desync.