[AmbularD]

I've seen several people ask, "If people can claim land just by building on it or putting pillars around it, and staff can roll back grief damage, then what's the point of even having claim blocks?"

Well, there are a number of reasons why claim blocks are still useful in spite of all that.  Here are some of them (feel free to comment if you've got a reason I missed...)

• Builds can be rolled back to exactly the way they were by staff, it's true.  Animals and villagers, however, though they can be replaced with others of the same type, can't be duplicated exactly.  If you want your fast brown horse or your librarian who sells Mending dirt cheap to be safe, protect them with claim blocks.
  

• Also, if grief is discovered a long time after it occurred, there's a possibility that it may be too old to roll back.  The server logs have been known to be wiped in the course of maintenance, making rollbacks to before that time impossible.  There's no guarantee it could never happen again Per Arrei, this will happen again.
  

• Valuable items like beacons attract griefers.  So do popular warps (which can also suffer honest accidental damage.)  Nobody wants to have to track down a staff member to come fix their stuff every time they sign on.  You can save yourself and the staff time and aggravation by protecting your valuables and warps with claim blocks.  In some cases, protecting an entire build may not be terribly practical if it's large or if you want it to be useful to the public, but you can still protect those parts of it which aren't intended to be interactive or publically accessible, or which seem particularly prone to damage or theft.
  

• If you build a large basement or underground complex fairly close to the surface, people may not easily be able to tell where the end of your build is, even if they're trying to respect the 100-block rule.  Noob huts and pillars and such can help, but they're not hard to overlook, and as we all know, it can take a little while for new players to catch on to exactly how claims and ownership work on HT.  Use claim blocks to secure your underground borders, and no one innocently trying to build a basement will break into your Batcave by mistake.
  

• For practical reasons, the 100-block rule isn't enforced deep underground, though griefing down there is still verboten.  If you've got a build down near bedrock and you want to make certain nobody will mine their way into it, use claim blocks.  (Caveat: Since claims reach from five blocks below all the way to the sky, if you do this, you always need to verify that you aren't inadvertantly putting a claim on part of someone else's surface claim.  If this is the case, it may be worth your while to contact the other player, explain what you're doing and ask them if you can work out a compromise; perhaps by one of you setting the claim and marking the other as trusted in it, for example.) 
  

• If the thought of someone tunneling under your surface claim gives you the heebie-jeebies and it's worth the trouble to you, you can also claim the area under your property right down to the bedrock...again, assuming nobody else has already built anything down there.
  

• For a variety of reasons, unsecured claims are just all-around more likely to be ignored, challenged or otherwise encroached upon than secured claims.  If you use claim blocks to secure an area which is rightfully yours under the server rules, not only are others physically prevented from messing with it, it's also much less likely that anybody will  question whether you're serious about it or your claim is legitimate.