first few places I worked had medicore to ok HR departments. They kind of kept stuff ticking over.
Then I worked somewhere with a good HR department and somewhere with outsourced HR back to back.
In the place with the good HR department, things ran a lot smoother. People had exit interviews (couple of bad apples were actually gotten rid of due to exit interviews by people going elsewhere) and there was protection and advice for people who were having difficulties. They gave me a lot of advice and support when someone I was managing developed a serious mental health issue- the person tried to attack a colleague during a psychotic break, then had a lot of time off before needing to come back gradually and with support like reconciliation meetings/workload adjustments etc. During a merger and restructuring process, people actually received decent settlements and support (both the people leaving and the people having to make decisions about who needed to leave). There were also a couple of cases were people who weren't performing well due to the circumstances of the merger (i.e. they had performed well at one of the two previous places but couldn't adjust to the new merged organisation), were given the opportunity to leave with a belated redundancy settlement and a good reference as "it wasn't their fault" rather than either be managed out or forced to try find another job whilst struggling. It wasn't perfect, but people did get a fair deal.
The place with outsourced HR was a nightmare. The (newish) CEO basically did whatever he wanted re hiring and firing and covered his arse later, they were always being dragged into employment tribunals, there was a huge pattern of people being let go just before their probationary period ended/legal rights started, so staff turnover was ridiculous. People were pushed out and bullied all the time. There was a small group of favourites clustered round the CEO who fawned over him (including gifts, invitations to sporting events, flirting and in one case, sexual favours). I lasted about 5 months, handed in my notice and never looked back.