OP, this can only be understand in context, not as a stand-alone issue. I think in most CP cases there will be a number of factors presented. Some will be obviously red flags - non-accidental injury, not feeding a child etc. And then there will be others that in themselves don't justify taking a child into care, but may together tell you a lot about what is happening. For example, home schooling, messy house, not registered with a GP, NC with extended family, persistent nits, refusing access to HV. None of these factors necessarily indicate bad parenting, and they would not trigger a CP investigation in themselves, but you can see that in an abusive situation they may take on a new meaning. For example, no problem with home schooling - but if children are being abused their parents may not want teachers (or GPs, or HVs) to see bruising.
We have so many CP threads on MN where people react to a single factor and shout indignantly, "Well my children sleep on a mattress! Does that mean the social workers will take them off me?" No it doesn't. And of course parents can refuse advice. But where there are serious concerns about the standard of parenting, and they are refusing to engage properly with professionals, and acting recklessly with regard to their children's welfare - then yes it's pertinent to CP. And with co-sleeping, if it is happening on a filthy mattress with parents who are addicted or violent or bringing new partners into the bed - then yes it would be a big red flag.