Sorry... You're off base.
You can only store one file in any given cluster (though multiple clusters can hold parts of the same file). Say you have a single byte file, using a 64kb cluster size it'll still take 64kb.
Now say you have a 65kb file. That's too big for a single cluster, so now you need two. Your file takes 128kb worth of drive space instead.
And a 129kb file takes 192kb (three clusters)...
And a 193kb file takes 256kb (four clusters)...
And so on and so forth.
Note that you can never waste more then 64kb per file, so the larger your files are the better efficiency you'll get. Basically space wasted = cluster size times the amount of files on the drive, so small clusters and large files are best.
On your PC, right click a large folder (such as Program Files) and select Properties from the context menu. Give the system a little time to calculate it's size. You'll notice there's two listings: "Size" and "Size on disk".
The former is how much space the files and folders take up. The later is how much space is actually used, due to cluster slack. Typically the later value will be higher (though Windows compression can sometimes reverse this).
Now consider how many files you could get onto a 1tb partition, and how a cluster size
sixteen times what NTFS can use would affect the wastage.
but it also depends on how many files you are storing, if you are storing emulator romsets and have tens of thousands of files then it can be a huge problem, if you are storing a few hundred HD movies its less of a problem, or a few dozen full dvd isos its hardly a problem at all