Why recognition matters
German law calls you a skilled worker (Fachkraft) if your foreign vocational qualification is equivalent to German qualified vocational training, or if your foreign degree is recognised or comparable to a German degree. The skilled-worker permits build on this definition.
§ 18 Abs. 3 AufenthGFor a regulated profession, recognition is mandatory. In a non-regulated profession you can work without it.
Anerkennung in Deutschland — Was ist Anerkennung?