You can know if the job is a good fit in advance
Disclosing your disability will allow an honest conversation with the potential employer about if the job is a good fit for you. You can determine if you can meet the requirements and see if the employer is understanding and open to working with you and/or providing accommodations in advance. If the position is too much for you to handle, or the employer clearly is not accepting that you have limitations or need accommodations then it is better to know before starting the job. If you wait to disclose you may have gotten the job only to later be subjected to discrimination and find out the position or company is not right for you. The disabled person in question may also find out that the job/company is a good fit. This would greatly reduce a person's stress. They won't have to try to hide their symptoms, which takes a lot of energy that could be better spent doing a great job at work. Not trying to hide your disability may also make the interview easier. It may be easier to sell yourself and effectively talk about your strengths and qualifications if you aren’t trying to avoid any mention of your disability. There are also some occasions where disclosing your disability may help you get the job such as if the job is with a disability-related organization, or you are applying for programs designed to recruit people with disabilities.
You know if you can do the job or not. If you can then you don’t need to mention your disability. Additionally, an employer might subconsciously not hire you because of your disability but then later once they know be understanding and provide accommodations. It is best to wait and see how the company is after you have been hired and shown your value.
[P1] Disclosing your disability will allow an honest conversation with the potential employer about if you can meet the requirements. [P2] You can see if the employer is understanding and open to providing accommodations. It is better to know if they aren't before you face discrimination at work. [P3] If you find out the employer is understanding and your stress is reduced, then you can more effectively complete the interview.
Rejecting the premises
[Rejecting P1] You already know if you are capable of doing the job. [Rejecting P2] An employer that might not seem understanding at first could be more compassionate and provide accommodations once they know you.