ZFS Boot Partitions

[spflanze]

In Step 2.3 of this document:
https://openzfs.github.io/openzfs-docs/Getting%20Started/Ubuntu/Ubuntu%2022.04%20Root%20on%20ZFS.html#step-2-disk-formatting
I see:

sgdisk     -n1:1M:+512M   -t1:EF00 $DISK

# For legacy (BIOS) booting:
sgdisk -a1 -n5:24K:+1000K -t5:EF02 $DISK

The way I read this n1 starts at absolute address 1M. and the absolute address range for n5 starts at 24K, and extends to 1024K or 1.024M. It looks to me like n5 overlaps n1 by 24K. Do I read this right? What repercussions would this overlap have?

The alignment option -a1 is used only for n5, and none of the other partitions in the document. Why is this alignment option needed only for n5?

Is n5 needed if the disks will only ever be booted in UEFI systems?