It is relevant when considering how much we should consider declining populations across many countries as a problem.

Some want to make this into an urgent issue we need to fix. I personally don't think population decline is a bad thing. Although I do think rapid decline is a bad thing because any rapid change is difficult to deal with. But aiming for a fertility rate of say 1.8 seems fine to me.

1.3 like some Asian countries are facing now is probably too low fertility rate. Although a this could be offset with immigration from areas which have not yet gotten fertility rate below or equal to 2.1