It's quite obvious that the German grammar is a very complicated
system; especially (but not only) the conjunctive and
conditional forms. Now the question is do Germans actually
speak according to the rules of their own language? If
you asked a German which one of the following sentences
are correct you'll find it hard to get a correct answer.
Most likely the answer would be that there is no difference.
sagt: "Sie kaufen ihm ein Auto."
sagt, sie kaufen ihm ein Auto.
sie kauften ihm ein Auto.
sie würden ihm ein Auto kaufen.
If you asked this question among 100 Germans probably
you'd get a 30 - 30 - 30 division.
A slightly different picture you'd get if asking about
sentences containing modal
verbs or the verb sein.
These are quite commonly used correctly.
If you now ask, why on earth should I learn something
that not even Germans quite use nor understand. Well,
you are quite right, it's up to you to wade through
the chaos or not. If you learn just for fun and to order
a beer at the Oktoberfest, you probably can forget this
chapter. If you are a student of German sciences
you'll want to know. For study, life and teaching this
could be really useful to know.