On Dw20? I think to prevent the use of normal quarries/filler. This to prevent performance issues. Use the ender quarry instead. It has the advantage of not destroying the location and leaving huge lag inducing holes everywhere. (Disregard this if you aren't talking about Dw20 but there is no way I can know what pack you are talking about, try to include this in the title next time )
Land Markers are banned because BC has a lot of bugs in its current stage. The first reason is the quarries are known to crash servers. The second reason is stated above, Performance. The Ender quarries are better in every way..
also never use robots, BC robots need to be banned on all 1.7.10 servers, their the BANE of tps, 3 of them are worse than 3 of my base networks from monster