When considering the use of hard links, what are valid reasons not to use hard...

The only valid reason not to use hard links is that they are specific to one filesystem and cannot point to files on another filesystem. This means that if you want to link files across different partitions or devices, you cannot use hard links. You have to use symbolic links instead, which are pointers to file names rather than inodes. The other options are either false or irrelevant. Hard links are available on most Linux systemsand traditional filesystems, such as ext4, do support them1. Each hard link shares the same ownership,permissions and ACLs as the original file, which can be an advantage or a disadvantage depending on the use case2. There is no such thing as suln, and users other than root can create hard links as long as they have write permission on the directory where the link is created3. When a hard linked file is changed, no copy of the file is created and no additional space is consumed. The changes are reflected on all the hard links pointing to the same inode4. References:

Linux Essentials - Linux Professional Institute Certification Programs1

Exam 101 Objectives - Linux Professional Institute2

Hard links and soft links in Linux explained | Enable Sysadmin3

Hard Link in Linux: Everything Important You Need to Know4