Variable rule on defensive holding?

[Bob Gill]

Two or three times in the last two seasons, I've seen something like this: A pass (or run) picks up 8 yards, but the defense is called for defensive holding. Rather than having the offense choose whether to take the penalty or the play, the referee simply ADDS five yards to the 8-yard gain.

At first I figured that was yet another new rule to give the offense more of an advantage. But in the same time -- including twice just yesterday -- I've seen several cases where the offense DID have to choose one or the other, the way it's always been.

So I'm wondering, is there some distinction that makes both of these calls correct? I mean, does the "take-one-or-the-other" rule only apply to running plays now, or something like that?

[JuggernautJ]

I think it's interesting that none of us can answer this once simple question...

The rules and the officiating are such that no one really knows how to play football anymore.
Good job, NFL!

[TodMaher]

Isn't it dependent on when and where the holding occurs? If the holding - in the opinion of the official calling the penalty - prevents a player from gaining additional yardage they will tack it on to end of the play?