With any legal matter, creating a documentary record is important. Because of the way most legal processes work, having documented evidence is necessary and if information is left out early on, that missing information could lead to your claim being denied. The risk is that you may be denied SSD benefits with a valid claim because you failed to supply the correct document or information.
Social Security Disability claims are often complex. If you do not have a specific medical condition, like cancer or heart disease that provides sufficient evidence of an impairment that by itself renders you unable to work, your claim may be denied.
The claims examiners may not be experienced enough to be able to "connect the dots" if you suffer from less well-defined ailments or conditions, or where a combination of conditions creates the overall impairment that makes work impossible. The Social Security Administration has a book with "listings" which are used when examining a claim, and the better your impairment matches one of these listings, the more easily your claim will be approved.
This is why it's essential that your medical records are complete. By supplying SSA with a full complement of medical records detailing your doctor or hospital visits, your treatments, your prescriptions and evidence of your completing treatments will all help to demonstrate to an administrative law judge that you have a bona fide disability that makes you eligible for SSD benefits.
If a hearing or appeal is necessary, your attorney can point to the evidence of your impairment from the various elements of your medical record, and can help clarify how the many pieces fit together to show the full extent of your disability.