It is described in the documentation of nftables as:
continue
Continue ruleset evaluation with the next rule.
This is the default behaviour in case a rule issues no verdict.
But I am curious as what might be the use cases of continue
One use case is, for example, it can be used in chain filters e.g. to match multiple connection states and set actions like established: accept, related: accept and new: continue where rules for new connections are defined in the following set for example ... Something like:
chain base_filter {
counter jump drop_filter
ct state vmap {
established: accept,
related: accept,
new: continue,
invalid: drop
}
... quoted from https://wiki.gentoo.org/wiki/Nftables
It's a convenience feature that mostly keeps coherence and consistency when writing/reading rules by humans (especially presets) and can be a needed feature in some cases when sometimes you might need to match a few, set action on some and continue on others.