The max existing value determines how many objects/mobs etc can load in the game. It
can prevent commands from executing. For example if you try to load 5 warriors in the
same room, but with a maxload of 4, then when you try to load the 5th, the game will
NOT execute the 5th command because it exceeds the maxload limit of 4.
M 0 11701 4 11970
M 0 11701 4 11970
M 0 11701 4 11970
M 0 11701 4 11970
M 0 11701 4 11970 * won't load because exceeds maxload
ALL of the existing items are taken into account, those in your zone, out of your zone and on PCs. So if you have a rare sword that loads 1/2 way through boot with a maxload of 1, but a PC has one and is online (not sure on storage), then that sword will NOT load because there's already 1 in game.
You can also use negative numbers. These count the number of items in the ROOM, not the
entire game. You can use this to effectively control repoping of mobs. Lets pretend we
have 4 guards who load 1 each at the corner of a castle.
M 0 51501 4 51501
M 0 51501 4 51502
M 0 51501 4 51503
M 0 51501 4 51504
Now at boot they'd load once each at each corner. But what if the PCs kill only 1 of them
before boot. On zone-reset only the FIRST mob would load, in r51501, and the rest would
be aborted due to max-load violation. So if the mob in 51503 was killed, on reset you'd
have 2 mobs in 51501, 1 in 51502, 0 in 51503, and 1 in 51504.
To fix this you could use the negative value as follows,
M 0 51501 -1 51501
M 0 51501 -1 51502
M 0 51501 -1 51503
M 0 51501 -1 51504
This way every room would always reload to 1 mob. Note - this can be trouble if your mobs
wander.
Finally you can set the maxload to 0, which means load at boot, and only at boot. This overrides any kind of maxload, or if flag. it's a great way to setup equipment if you don't want PCs to farm it.