A permalink or permanent link is a URL that is intended to remain unchanged for many years into the future, yielding a hyperlink that is less susceptible to link rot. Permalinks are often rendered simply, that is, as clean URLs, to be easier to type and remember. (Thanks, Wikipedia)
I've committed to maintaining my personal permalinks (58 as of the time of writing!) for the foreseeable future. This way, I can direct people to my permalinks rather than the Ghost/any other service's defined links, in case I move away from that platform, my content still follows me.
This approach also opens other cool doors, like having multiple domains that point to the same places.
For example, both of these links will take you to my Home Server blog post.
Hopefully this shows you why permalinks are neat, and why you should use them.