This is one of the ways to do so, yes. However in case of case you do not need to pass first, so you could do:

case {bar, baz} do
  {_, 12381} -> {:ok, :ignored}
  {list, _} when length(list) -> {:ok, :ignored}
  _ -> ExternalService.call(attributes, bar, baz)
end

Or you could squash the two cases:

case {bar, baz} do
  {list, num} when num == 12381 or length(list) > 100 -> {:ok, :ignored}
  _ -> ExternalService.call(attributes, bar, baz)
end

However in that case whole pattern matching is needless, so we can do:

cond do
  baz == 12381 or length(bar) > 100 -> {:ok, :ignored}
  true -> ExternalService.call(attributes, bar, baz)
end

Or you could use if macro if it is clearer for you:

if baz == 12381 or length(bar) > 100,
  do: {:ok, :ignored},
  else: ExternalService.call(attributes, bar, baz)

EDIT:

@tushar as length(baz) is used only once then it is much better to not cache it, as if baz == 12381 the length(baz) will not be called at all which can save time, as counting length of the list can be needlessly expensive for long lists.

But is it ideal to convert it from multi funs to case block / cond block? Or it’s just a matter of preference?