Sweet question

Briggs didn't intend for or want him to be killed. Briggs tried to keep Davis and Sweet off the arrest team that was going to take down Palancio -- remember he protested that they were rookies who lacked enough experience. The problem for him was that Harry specifically requested Davis and Sweet, and Briggs didn't really have a good enough reason to deny the request. And if he pushed back too hard against Harry's request, people might wonder why it was such a big deal to him. Running an unauthorized murder squad on the SFPD was something he was anxious not to draw any unwanted attention to, so he had to concede. He then tipped off Palancio (and it was almost certainly Briggs personally, as Grimes or Astrachan, had they known anything about it, would doubtless have warned Davis and Sweet what they were walking into).

Why tip Palancio off? Simple: Briggs didn't want Palancio arrested; the idea was to get him and his gang killed in the ensuing shootout by making them think they were being set up for a hit instead of being arrested. Once the shooting started, the police would call as much backup in as needed until all the bad guys were dead. Briggs sent Harry because, while he disliked Callahan he respsected his skills, he knew Harry was very likely to still get Palancio despite the tip off. And if Harry got killed in the effort... Well, so much the better. He'd be rid of that headache at least. Doubtless he hoped Davis and Sweet would survive -- they were highly trained veterans and highly skilled shooters after all. But he had to accept the risk, and indeed, Sweet got killed.