For large disks you might feel the need for a larger block size to boost performance, but looking at the DDB files, there are also a lot of small files. If you put the small files, for example 16KB, in a block of 128KB then you have lost 128-16 = 112KB space. This doesn’t seem much, but when the amount of files get larger it will be noticable in your free space.
When you have larger files this would be less of an issue, then you only have a possible loss at the end of the file. Unless hole drilling is used, but that's a whole different story which I won't go into right now. When a file is bigger, for example 9,6MB, you have 9830,4KB. This results in 9830,4/128 = 76,8 blocks so actually 77 blocks. This is a los of space of 0,2 block = 128*0.2 = 25,6KB
As you can see there is quite the difference in waist of space for a single file.
Additionally there are concerns regarding the fragementation or amount of file extents, the more fragmentation or file extents needed the more I/O is needed and thus lowering the maximum performance.
There is a lot of details to cover in order to fully grasp the concept, too much for me to explain in this thread. But hopefully these articles will give you some insight:
A contemporary investigation of NTFS file fragmentation - ScienceDirect
Best_Practices_Eliminating_Fragmentation.pdf (adldata.org)
Everything You Need to Know about SSDs and Fragmentation in 5 Minutes - Condusiv - The Diskeeper Company
Hope this helps.
