What is the meaning behind saṅghānussati chant?

For the meaning of saṅghānussati in advance, see Part II—Concentration (Samádhi) CH. VII SIX RECOLLECTIONS Recollection of the Saṅgha page 215.

We should be used with the tree refuges according to Sutta. Ma. U. Sevitabbāsevitabbasuttaṃ:

It was said, "Sāriputta, I say, persons are also twofold those that should be used and not used" On account of what was it said by the Blessed One? Venerable sir, when using certain persons demerit increases and merit decreases, such persons should not be used, when using certain persons demerit decreases and merit increases, such persons should be used. It was said, "Sāriputta, persons too are twofold, those that should be used and not used. " It was said on account of this.

Why? Sutta. Khu. Jā.(1) Vīsatinipātajātakaṃ Sattigumbajātakaṃ:

“To whomsoever, good or bad, a man shall honour pay, Vicious or virtuous, that man holds him beneath his sway.

“Like as the comrade one admires, like as the chosen friend, Such will become the man who keeps beside him, in the end.

“Friendship makes like, and touch by touch infects, you’ll find it true: Poison the arrow, and ere long the quiver’s poisoned too.

“The wise eschews bad company, for fear of staining touch: Wrap rotten fish in grass, you’ll find the grass stinks just as much. And they who keep fool’s company themselves will soon be such.

“Sweet frankincense wrap in a leaf, the leaf will smell as sweet. So they themselves will soon grow wise, that sit at wise men’s feet.

“By this similitude the wise should his own profit know, Let him eschew bad company and with the righteous go: Heaven waits the righteous, but the bad are doomed to hell below.”