if you play a G D C vamp, you're pretty much playing a blues (I V and IV degrees) so the pentatonic fits perfectly over each chord, but you need to have target notes, that fit better. Eventually, you'll learn how to fit each chord's pentatonic, so you'll switch the set of notes that you're playing along with the chord. That's called playing the changes. Jazz cats do that to the extreme, since some progressions change keys every bar or so.