I have seen this in many Anti-Lag scripts (That which do not work), where it does
if (game.Debris.MaxItems > .174) then game.Debris.MaxItems=game.Debris.MaxItems*174
, but when it does to that part, it does not change MaxItems, how can I change MaxItems, why is it there, and/or what is it used for?
The Debris service is/was a service which kept track of parts that you knew were "debris" and could be cleaned up after a short time.
I don't know whether or not they still use them, but a classic example of debris were the parts that fell off after shooting something with a paintball gun.
The Debris service would delete parts once there were more debris than the "MaxItems" number.
Almost nothing uses the Debris service anymore, so you really don't need to worry about it. It should still function completely correctly, though, so if you want to use it--go ahead!
That particular line that you quote makes no sense whatsoever. There's no such thing as an anti-lag script so the things that claimed to be them usually did strange / pointless things to confuse people into thinking they were accomplishing something.
You should just set MaxItems to some reasonably number (probably 100 or 1000 or perhaps smaller, depending) on the service itself, probably, by the property window, instead of by a script.
If you're setting it by a script, though, just set it to a number.
http://wiki.roblox.com/index.php/MaxItems_(Property) Check this out, it should help with the what parts.