Say you’ve chosen 2^n size of something initially. If you decrease it, it may sometimes not help at all - you usually have 2^k parallelism cores for SIMD (same instruction multiple data) processing, and with regard to saved memory - there are downsides with these “unaligned” zones of arbitrary size too. If you increase the size to 2^n+1 instead, this usually results in a new memory block allocation, so it is not efficient in many cases.