This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Pit Bulls and Parolees
One of the most potent was when Tia found out that she had to decide right then and there whether her husband would take a deal for a 15 year prison sentence or go to trial and risk a life sentence. They chose to take the deal.
When Tia's daughters come back from New Orleans with a live rescued dog and the remains of one who died alone under an overpass, and Tia takes them up the hill to give her a final resting place. The real Tear Jerker hits when all the dogs start howling in unison as if they knew what was going on.
The start of Season 3 completely negating the heartwarming finale of Season 2, as the community they were going to move into protests their building a shelter. By spewing all the hateful stereotypes about the breed and the workers that Tia and the Villalobos Rescue Center have been fighting to prove wrong.
And then happy tears when the community in New Orleans welcomed them with open arms.
And every so often, a parolee can't pull their lives back together despite given the opportunity to do so with what is probably the best chance they had. Tia's disappointment whenever this happens is pretty heartbreaking.
Prada, who got into a fight with another dog before coming to Villalobos (it was a German Shepard and the case was high-profile), can not be adopted by executive order. It was that or she would be euthanized. Despite the German Shepard's owner admitting it was her own dog who bit her and an attorney working on it for fourteen months, all they can do is kennel her for life.
Chong, a dog that had nearly died from cancer before miraculously recovering and going into remission, had a relapse and died at the vet's office. When Tia gets the call, she is literally brought to her knees with grief.
Made even more poignant later on when the twins are spreading Chong's ashes and his brother Cheech starts whimpering, as if he knew who it was.