@TheFerrett wrote a short piece claiming that this line is mainly useful for monogamous people: "Never Make Someone Your Priority When You're Only Their Option" https://fetlife.com/users/338073/posts/5468748
I disagree.
The point of the saying is to remind people to check that their expectations for the relationship are similar to their partner's expectations.
If one person expects to get together every week, and the other one prefers once a month, or
if one wants to be a 24/7 slave while the other is just looking to top once in a while, or
if one keeps their calendar free for possible one-on-one time, and the other is only occasionally willing to fit one-on-one time into their busy schedule
... those are likely to lead to frustration and disappointment for the higher intensity person.
That's the point of the saying: to assess whether you can be happy with what your prospective partner (monogamous or polyamorous) wants to offer you.
It doesn't mean that every relationship has to be a top priority.
It means -- if your partner treats the relationship lightly, are you okay treating the relationship lightly too?
SOURCE: https://fetlife.com/users/419868/posts/5469397