Than

Always essential: My husband was more upset by our argument than he wanted to admit.

So Long That

Always essential: The meeting was so long that we could not stay awake.

Using Commas With Phrases

Use commas to set off nonessential expressions--words, phrases, and clauses that are not necessary for the meaning or structure of the sentence. You can tell whether an expression is nonessential by trying to omit it. If the sentence makes sense and is structurally correct, the expression is nonessential and should be set off by commas.

Nonessential: Let´s talk to Bob, who has experience in this area.
Essential: Let´s talk to someone who has experience in this area.

As

Essential: The results of the mailing are "as you predicted they would be."

Nonessential: The results of the mailing are disappointing, "as you predicted they would be."

Until

Always essential: I will be at my desk until 4:30.

No Matter What

Always nonessential: The project will not be completed today, no matter what my manager wants.

As ... As

Always essential: He talked as persuasively in person as he did by telephone

All of which

"All of which" always introduces a nonessential phrase.
My term papers, all of which have been completed, were on a variety of topics.

Some of Whom

Always nonessential: They interviewed ten applicants, some of whom are qualified.

Because

Essential: She left "because she had another meeting." (Here the phrase is needed to complete the meaning.)

Nonessential: I need to have two copies today, "because I am leaving tomorrow." (Here the meaning is complete without the phrase. The phrase is just extra info.)

For

Always nonessential: He read the book, for he wanted to learn about England.

None of Which

Always nonessential: We ordered five tacos, none of which have arrived."

After

"After" always introduces an essential phrase.
He called after you left.

Whereas

Always nonessential: I like chocolate shakes, whereas my husband prefers strawberry.

Although

This always introduce nonessential phrases.
She has joined a gym, although I don´t think she´ll really use it.