The 1 MiB (2048 * 512-byte emulated block size) choice is a great catch-all for various hardware storage configurations. Since file system data structures are generally aligned with the partition start point, this can be important to maximize storage read/write speed.
For example:
RAID may use data stripes ranging from 16 to 256 KiB in size. 1 MiB is an integer multiple of this, so starting the partition at 1 MiB is compatible with the underlying RAID model.
SSDs typically have an erase block size of 128 to 256 NAND pages, which depending on the drive might be 256 KiB or 512 KiB. So here again, starting the partition at 1 MiB is compatible with the underlying SSD storage characteristics.
Advance Format 512e spinning HDDs have a 4 KiB physical block size, and again, 1 MiB is an integer multiple (albeit a rather large one) of this.
So while if you have an AF drive and are partitioning as GPT, you might be perfectly happy with your first partition starting at LBA block 40 (an integer multiple of the 8 logical blocks in each physical block of your HDD), hardly any real-world storage is lost by just starting at LBA block 2048 (1 MiB), which is just a more flexible value for partitioning software to default to since it is suitable for pretty much any hardware configuration.
