Its more that a company will use this information to possibly overturn a declined application - although companies are cautious when it comes to the information written there as it comes from the individual, they would prefer proof of what has occured - if you can supply this state it on the NOC.

 A NOC will not be detrimental to your credit file as your file already shows the bad credit you have - it just gives the reason for this bad credit. Without this your application could be declined outright because it fails their credit score, but if you have a NOC due to something that happened, your application will probably be refered for further investigation. The lender then reads the info on the NOC and will then make a decision whether to lend or not.

 Usually the application would still be declined, but I know of cases where the information in an NOC has allowed the lender to proceed with the application as the poor credit was an exceptional circumstance.