[Drumstix42]

The things that are claimed to cause lag are what people use in hotbars/macros part of the standard UI. People use "megamacros" still, and it can be like..... Cast 10 items at once.

At one point spell casting/queue or something like that was moved to client side to reduce strain, but I don't think it can really work 100% because of all the items, and clickies, and insta cast abilities.

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In some cases, people may be using macros like this in click buttons, but it's really no difference than having 10 hotbars open with mega macros, like a lot of people do.

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Food for thought about EQ2 lag:
Determine the number of chat messages that gets sent to/from a person in combat on average, multiply it by 24, and then send it to all party members in the raid *constantly*.
24 people sending data to the server that gets sent to all 24 people each. Just look at the data transfer graph during combat...
Then add in all the other raids, and groups, and people playing. I dunno. I just think there's like a million times more chat spam than needed.

Some people claim a full raid force using default UI may benefit, and I would probably agree, but only because any extra windows in the UI lower your FPS, lower FPS lowers your UI/keyboard response time, and this probably has people trying to do less because they're not clicking things as effectively. I dunno. I think it's conjecture, but all in all: I think the game is just a mess and that's the real problem ^_^