Like RJ, tho I'm very much a beginner, flexibility is really good. Examples are, an MR or ML with AMR and AML secondary roles means you can slip them back and forward without subs or you could use AMR or AMLs with AMC secondary and then they can go from wide to narrow. Similar options can be used defensively with some having the option to be pushed forward or sideways (or midfielders back).

For me, 4-4-2 is a sound base which you can then develop as you gain multi-role players.