Yes,it is indeed the best thing to have all things considered, which is why IPSEA argue so ferociously for them but still not a panacea.
Statements used to be given out like lollipops until the true cost of them became apparent as well as the implications if parents decided to chase up woolly promises (see 'Landmark Judgements' on IPSEA websites.)
Now big move to reduce them which I am not personally against, as most are useless. Centre for Policy Studies has an excellent paper on the epidemic of nebulous 'Special Needs' endemic in UK and the lack of accountaBILITY in addressing them.
MOst stuff is pretty shoddy, whether in a statement, IEPorn SA + or whatever other euphemism is currently used by your LEA.
It's shoddy because generally it is not Specific, Measurable, Attainable, Relvant and Timebound (SMART)
If it is SMART it will be good if not, it won't. Simple as that.
To compound the issue, parents often fighting for provision that isn't suitable, or, even if available, likely to be of use in improving whatever it is they are concerned about.
Take SALT (my profession). Some parents really believe that spending specific amounts of time 1:1 with a SALT will bring about measurable improvements in their kids' communication.
95% of time it won't. Kids whose communication is compomised need to be with their peers in school as much as possible and for the SALT to help the teacher in the classroom with this. It really wouldn't make any differense if they has 3/4 hours of 1:1 SALT time a week. In many cases, it woudl exacerbate problem.
Quality is not synoymous with quantity.
Generally I notice a strange inverse correlation-the thicker the file, the less anything useful is likely to have been done.