Why are "sectors per track" still relevant on a modern OS with modern drives?

This is an HP ProLiant server with a Smart Array P420i RAID controller. My immediate advice is to not change any of the default configuration settings unless you have a very specific reason to...

In short, don't worry about it.

The concept of sectors/tracks in the context of this controller and disk geometry isn't very useful here. Lots of layers of abstraction; useless unless you have a specific alignment issue to tackle or need a larger boot volume on a legacy OS. Enabling the Max Boot feature (>4GB boot volume) on the Logical Drive increases the sector count from 32 to 63.

HP's description of the option:

This option specifies the number of sectors that are to comprise each track. Logical drive performance is likely to decrease when 63 is specified. This setting applies if older operating systems such as Windows NT 4.0 are installed and if the boot partition is greater than 4 GB. Most modern operating systems handle greater than 4 GB boot partitions and no longer require this setting. Please check the Operating System documentation for further information.

I wouldn't touch it.

SAS disks support a SCSI command set. The commands utilise a block as the unit of access. The only reason I can think of having to indicate the number of sectors on a track would be to permit performance optimisation in the case where the controller needs this to improve cross track performance and is unable to query the physical geometry of the disk from the drive.

Of course most disks have different numbers of sectors on a track at different points on the disk to increase average data density.

I don't recall when I last provided this level of detail on drives, and never in the case of SCSI disks.