If you're having trouble with being griefed, the mess can always be undone by a member of staff (Unless it's in the mining world). If you don't want to have any chance of being griefed (or at least a very minuscule one), you can join a town.
I tried a server using an autolock plugin, and it didn't really work very well. For example, say if I was to make a 1x1 tower to get out of a small hole, then later on that day somebody tries to make a house in the same area, only to find out that they cannot replace their floor due to the aforementioned dirt pillar, wouldn't that be an unnecessary inconvenience? Sure, it stops people destroying blocks, and so long as a member of staff is there to clean up any randomly placed blocks / griefings, it's a great plugin. But surely if a member of staff is online and the plugin is not in use, everything would would be pretty much the same as if the plugin was.
If you real can't be bothered to read everything above (and I don't blame you for that), in short I think it just makes minor griefs (involving placing blocks rather then destroying them) more of a big deal.
Anyway. That's just my opinion