If you are applying for just SSI, then yes, all the SSI rules are really important.
If you are applying for both SSI and SSDI, it is a little more complicated.
There ae three reasons someone might apply for both SSI and SSDI:
One: To Survive
🐬 You are expecting that your SSDI check is going to be less than $735/month. You are applying for SSI so you have enough money to live.
Two: Just In Case
🐬 You are expecting your SSDI is going to be over $735 per month. You won’t be getting a monthly SSI check. But you know a secret: There is a special loophole where sometimes people get an extra five months of SSI backpay. You won’t know if the loophole applies to you until after a decision is made.
Three: No Clue
🐬 If you have no idea why you are applying for SSI, welcome to the club of just about every other person that has ever applied for SSI. You can figure out about how high your SSDI check is going to be by calling Social Security or even better read: How Aster Figured Out How Much Actual Benefits He Would Actually Get
Do I Need to Know the SSI Rules?
🐬 If you are applying to survive, hell yes, these rules matter and they matter a lot. Learn everything you can.
🐬 If you are applying just in case, my guess is you probably don’t want to give yourself a headache learning all the SSI rules for something that may only be five months and usually won’t happen at all.