So, it might be good to use against a run-out player to slow them down?
This used to be the "common knowledge." I used it all the time. Anymore I don't believe it. Generally a run out player has more table knowledge than someone who can't run out. This means, while you might slow them down a bit and maybe get a turn at the table, they still break clusters better than you and have offensive firepower to get out. A smart player, which most good players are anymore will just out move you until the time is right.
Now, if you were playing a really dumb and purely offensive player with no safety knowledge, it might help you beat them. But the truth is that anymore unless you're playing in some bar league you'll not see a player like that. Players with the skill to run a rack mostly have all their ducks in a row nowadays. 2 Decades ago sure, cluster the balls. Now the bastards have gotten smarter.
If you're playing a similar level player that you are and you can't run more than 4 balls, it might favor you but even that is questionable if you can't break clusters.
I think at best it's situational advice. I see this all the time in our town leagues: The older ladies and lesser skilled casual players will do second ball break. It extends the innings but they still get tromped into the ground by better players. The absolute worst matches are between two lesser skilled players, neither of which can deal with clusters, yet they insist on second ball breaks. It makes a 10+ inning match where you might as well flip a coin.
The best 8 ball I've seen lately is the Ultimate Pool USA format. You have to get a 3 point break. A combination of made balls or balls past the center line of the table. It gets rid of slow play, and when you're on a shot clock and a match clock and might be spotting 4-5 games you literally don't have time to play pitty-pat pool. You have to either run out or have a plan. I love 1P but on a weeknight league I don't want to be there till 2AM. There's not near as much just bunting balls around and buying time, because time is one thing you don't have. The funniest part is if you do an illegal break (doesn't meet the 3 point rule) you lose the break and your opponent breaks. Sometimes they too do an illegal break so you get it back. But... it's alternate break, if you lose your break and they break that rack legally, they still get to break on the next rack. It sounds nuts but it really does improve the game, gives you a bit more urgency which is something pool leagues can lack.
Might be a dick move but I find it amusing, and generally after that they will rack tighter. Even league players who are known for giving slug racks usually won't repeat the offense if you say it loud enough for the spectators to hear. 
