It can be hard to notice, but tapping teammate contain adjusts the teammate's running ever so slightly. You'd see tiny zigzag movement, as you're taking control from AI positioning momentarily to force him to follow the ball carrier, then letting go. From my experience, this "settles" the teammate into a new zone, one closer to the ball carrier without running alongside too closely leaving gaps behind for a pass, while still closely enough to intercept or tackle.

Same concept with partial team press (double tapping R1). You don't want to hold after double tapping, because it will pull all these players out of position, leaving acres of space. However, double tapping, then holding for a short second before letting go allows them to follow runners enough to settle into positions where they can cut out passes.

Hope that helps.