Clumps
Clumps groups XP orbs together into a single entity and sends it to the nearest player to reduce lag. On top of this, it also makes the player immediately collect the orbs once they touch the player, so you are not stuck with a bunch of orbs in your face. With this add-on, you don't have to worry about XP orbs and XP farms causing lag in your world/server.
Arrow shot:
Pig dies:
XP obtained without going near the pig:
For example, as you can see in the above images, that as the pig died, the XP orbs dropped by him were clumped and sent to me instantly. Similarly, every XP orb dropped on your world/server will be clumped and sent to the nearest player instantly. For better understanding, I recommend watching the YouTube video linked below.
Installation
Do I have to install it in client or server side ?
You have to install it in server side (behavior pack).