Install dual boot Windows 10 uses the most basic partitioning scheme. It creates a swap partition, and a partition to hold the file system. And on EFI systems it uses the EFI partition on the first internal drive for installing grub.
For many online partitioning guides, the poster is asking how to create a certain set up; for example, separate home partition, server partitioning schemes, USB boot, preconfigured partitions, etc. Also many, recommend custom partitioning schemes for the reasons listed in the next section. Thus, the do something else option is needed to set up partitioning that is different from the default.
There is no difference in performance. Some of the most popular reasons for custom partitioning are:
Specify the size of the swap partition. I forget how the installer determines swap partition size, but on larger drives, it can be excessive.
Separate /home partition makes it easier to snapshot system files, or do reinstalls without copying a lot of personal files.
Separate data partitions can be mounted into various installs without the need to copy large amounts of data into each.
I’m not sure why, possibly for departmentalization, but server installs tend to use separate partitions for many system folders.
Separate /boot partition is needed for full disk encryption or RAID setups