I'm not sure. A couple of seasons ago I had one (back and across) until I realised it was playing to my weakness by being on off stump, i.e. missing straighter balls when my strength is the offside.
I was very well balanced and still early last season and scoring (for me) consistent runs, taking a middle guard. Towards the end of the season my runs tailed off in correlation with (unknowingly) falling over, causing me to be bowled or lbw.
With a few weeks to go our skipper brought in Mal Loye, who he knows through work, to do an outdoor net with us. He had his sidearm and, first ball, had me plumb lbw. Second ball the same. Third, he paused at delivery and I was falling over. The first thing he tried to do with me was a trigger - directly backwards then step forwards. In a nutshell, I was all over the place!
Long story short, I've been at Vitas for nets and working with Jake on a middle guard and staying upright, eyes level and going towards the ball. I feel much more comfortable doing that than worrying about timing of triggers. I understand totally if players have grooved it to perfection, but (as someone who's tried it for some time), it's not for me.
I think it feels like I have to think about when I perform the trigger, so I'm not focussed on the bowler and then the ball. I've clearly never grooved a trigger for it to be unconscious competence. I probably could over the course of a winter, but I genuinely don't see how a trigger would help me at the level I play at. I've scored my highest scores by staying upright, eyes level and watching the ball.
That said, there will be forumites with a lot more ability than I to provide their own insights!