Compulsion = you have to do it. Things that are compulsory for parents in this country in relation to children are registering their birth, ensuring they get an education (though not necessarily in school) but primarily securing their physical, emotional and social well-being until they reach adulthood and can do it for themselves.
That is it.
Optional = you don't have to do it.
We are incredibly privileged in this country to be offered many services that help to ensure our children are healthy and educated. But many of these are offered on an optional basis such as vaccinations, developmental checks, state education, access to NHS healthcare (but you can choose private care if you prefer).
The implications of refusing these things are not that anyone will compel you to do them. Hence Not Compulsory. Loads of people don't do them, the vast majority of them are people fulfilling their primary responsibility as parents - to secure their children's welfare.
However, in the small class of people who are neglecting their children there may be more children who do not get routine vaccinations or developmental checks or get supported to attend school. Seeing a pattern of non-attendance at baby clinics, vaccinations, developmental checks and school would be rather worrying? In some cases it might be because the parents are ensuring their child's well-being through other health and education services or are very confident of their own judgment. In some cases it might be because the parents are making terrible judgments and the child is at risk. So in those cases I'd be grateful if HV's both tried to get in touch with the family and if that failed notified SS that they had concerns.
There are also children being actively abused by parents who Do take their children to developmental checks, vaccinations, make them attend school, even develop bizarre and elaborate accounts of illnesses they don't have to mask the injuries they have sustained through abuse (this is very very very rare and unfairly stigmatises many parents of children with genuine but obscure illnesses).
But this kind of paranoia about developmental checks is unhelpful. If you don't find it helpful ask for it to be cancelled again and don't worry about it. Nothing about the way you are caring for your child suggests you have any reason to be anxious.
Social services have far better things to do than investigate every single child in this country who does not have an age 2-2.5 check-up.