Especially when using prepositional phrases and complex sentences, leaving out a comma can lead to confusion, or even an absurd statement. Read these sentences without commas.
Even before spring leaves start to appear on the trees.
When does spring leave?
If you wash Jesse will dry.
Why are you washing Jesse?
While we were eating Audrey announced her big news.
We were eating Audrey?
Before you vacuum your sister needs to dust.
Sisters don't need vacuuming (usually!).
Now read the same sentences with commas. They make much more sense!
Even before spring, leaves start to appear on the trees.
If you wash, Jesse will dry.
While we were eating, Audrey announced her big news.
Before you vacuum, your sister needs to dust.