To expand on what the others mentioned, it can be used to lure a victim of abuse back to their abuser or soften them up for the next blow.

I won't talk about the specifics of how I know this phenomenon, but the rough pattern usually looks something like this. I'll use the "narrative I" for the position of the abuser, because that feels more comfortable to write.

Imagine I'm some person of authority or admiration, be that a parent, a cult leader, a partner, a friend, or even a boss at work. You care about my approval and support, whether out of dependency, affection or convictions. The exact motivations may differ: You may be dependent on a parent's support even as an adult or hold the conviction that you have to love your parents no matter what. Your cult may (and usually will) have isolated you from other social contacts. Your boss used to be really nice or even a friend and maybe still is, outside of work. Whatever the reason, you want me to like you.

If I treat you like shit, make demands, then punish your disobedience by withdrawing affection, support and approval, that hurts in one way or another. You're used to my affection, perhaps relying on something I'm giving you or some promise I made, and suddenly that has been taken away.

Once it starts to relent and you get used to the new "normal"¹, I suddenly start "loving" you again, maybe giving you nice things, saying nice things, promising nice things. If I'm an estranged parent, a partner or a friend, I might suggest doing something nice together, meet you for coffee, a lunch or drinks - my treat - to chat, ask how things are going, sympathise with your struggles, offer to help, promise you to cover that expensive repair of your car. I reassure you that things will work out, I praise you for things you're doing well, validate where you're insecure, hit all the right buttons to make you feel better. A boss might praise your performance, make a point of talking you up while you're in earshot, promise a raise etc. A cult leader might restore whatever grace you have fallen from, promise salvation, pray for you or whatever else passes for approval and support in the cult.

Most people are suckers for nice things, and even if you tell yourself you'll just take the nice things and not trust me any further, you're still receptive to what I say...

...until the next punch (whether emotional or physical) comes. I express disapproval with something you're doing that I want you to stop, request your help, disparage your partner of many years, make decisions on your behalf, ask you to work overtime "just this once", expect you to follow along with some cult activity, whatever may fit the given dynamic.

You might (reluctantly) obey at first - that's the price you pay for the nice things, but so far, it's still worth it - until the demands start tallying up and the rewards diminish¹.
I totally forgot to send you the money for that repair, I'll do it later, but right now I need you to help me with this thing. The raise is being held up on formalities, but I'm sorting it out and it should be coming by the next quarter. In the meantime, could you look into this? I just don't have the time or energy to do this right now, but I promise, I'll do it when I have the time.
You get the picture.

You start reevaluating pain vs. gain. Is it still worth it? Eventually, you're fed up. You start making excuses why you're not doing some thing, your work ethic declines, you become dispassionate, withhold whatever validation I'm expecting of you. I get angry with how ungrateful you are. you can pay the damn repair yourself if you can't even do this "little" thing for me, I'm not giving you that money while you're with that partner or hang out with that friwnd who I'm convinced is only out to take your (my)² money. The raise is off the table. You'll go to hell.

I won't entirely cut you out, of course, while you're still useful to me (or I expect you will be at some point). You don't entirely cut me off because of the reasons mentioned earlier, because you hope I'll turn around again some day. And so the cycle repeats.

From the outside, it's easy to say "just leave". It's often the reasonable solution in the long term. But emotions are complex, change is scary and sometimes, it's easier to stay with the devil you know.

[1]: If I'm particularly canny, I'll push that line in such small increments that you barely even notice it's creeping and you're getting less and less. Just one more poisonous comment you have to endure, one more loaded question, one slight annoyance at not having read my after-hours email yet (I won't say that I'd expect you to, but my face says enough). You dismiss it, but it leaves you slightly more drained every time.

[2]: Particularly with abusive parents or partners, there's a phenomenon where they'll consider you their property, and by extent, everything they give you is actually still theirs to take back at any time.