Aye so, I have recently figured out that you can, in fact, claim land! To do so, all you need money and either a diamond or emerald block. First, you must place your chosen block in the area you would like to claim, enter the command /lock and left click the diamond or emerald block, and you will then claim a small area near that block. The Emerald block will claim a 9 x 9 x 9 area around itself. The Diamond block will claim a 15 x 15 x 15 area around itself. This will only keep your land safe, not your chests. Do not use this to claim other peoples land or to troll. Enjoy
You know this is explained in the museum for everyone to see, right? Secondarily, yes, towns are a better way to go for multiple reasons. These blocks count toward your lock count, so if you have a lot of locked chests and then start locking these blocks to "protect" your area, the costs will keep going higher. Imagine 2000 rupees just to protect a 15x15x15 area! That's 40 days of town upkeep for a town plot (which goes from bedrock to build limit and is 24x24 - significantly bigger). So yes! You are correct! You can protect a tiny little plot of land with locked blocks! But there are definitely more efficient ways to protect more space.