If a command block attempts to run a particle command that would not be seen by a player (e.g. there is nobody online and the particle is in spawn chunks) this message is printed in the server console regardless of gamerules:

com.mojang.brigadier.exceptions.CommandSyntaxException: The particle was not visible for anybody. 

This can lag server control panels which attempt to parse the log output and overall leads to an unreadable server console.

To reproduce:
start a server instance
generate a flatland world with the spawnpoint at (0,0)
place a repeating command block
insert this command:

particle enchant -35.0 65 0 0 1 6 0 20 

Look at the server console.

Note: This does not appear to be true for functions.