Have you ever made a huge contraption with a bug in the middle of your machine and the only way to fix it is to demolish the entire machine in order to get to that bug? Now that's no longer necessary. Just fly through the blocks.
This is basically a no-clip plugin. This is how it works: it removes all bock around you within a certain radius and places them back when you move away from them.
Put the jar in your plugins folder and reload the server.
/ghost - toggles ghost mode
ghost.noclip - can enable noclip, default is op.