So far as I know you can't opt in or out of having a Health Visitor.. but they are there to continue your aftercare after the midwives 11 days are up..
The HV will come round initially to introduce herself before you have the baby..
She will take a look at the conditions in which you live (I thought they had stopped doing this, but the last HV I had round for my son wrote down in her notes 'good conditions') - although I think it's dependant on area, tbh.
She will also ask about your history of PND, anything like that, any possible problems you can foresee. She will then come round again once the midwives have stopped to make sure you are ok and to ask you again about your mental health, how you are coping, whether or not you have support etc.
She will give you all the info you need about visiting times for the clinic etc and what they do there. She will weigh and measure bubs too.. and she will give you all the info on injections/immunisations, feeding etc. She is there as a point of call for you, essentially - anything you're worried about, is baby gaining enough weight etc, any other concerns you might have, she's the one to go to with them.
As someone esle said, if you don't like your HV, you can get them changed. It's just the same procedure as with your midwife, if you're not happy with them, then there's absolutely no point in them giving you care, because it won't be mutually beneficial to anyone, least of all bubs.
Health Visitors can be a godsend, especially for new mums, or even second time round mums! Mine have always been amazing when it comes to PND, I've even been able to request certain HV's from areas just out of mine to come see me as I've made such good friends with them. They aren't to be shrugged off lightly, although, if you find you're just not bothered with getting bubs weighed every week, or measured or whatever, then there is no obligation for you to go to see them after the initial visits. They will check on you again in 6 months or so, in my experience.. They are also absolutely brilliant with any issues you might have with older children too.
All in all, HV's are there for you.. and your wellbeing, but if you don't want to bother with one, you only have a couple of visits to get through and then they leave you alone anyway.
