My son and/or I receive some benefits (and not others). We're not in the US, so unfamiliar with SSD and SSI, but here's some of our experiences with government support/subsidies in general:
-some of the supports are attached only to a condition, i.e., not savings-or-income tested, just medically-tested
-some of the supports are restricted to specific uses (e.g., rent, or medical therapy) and essentially go directly to the service provider
-some of the supports are income-tested only
-some of the income-tested supports are tested via the previous year's tax return, some by the previous month's income, and some by the previous six months' income (basically, we would have to do the equivalent of annual tax accounting up to 15 times a year, which is difficult on a variable income)
-some of the supports are savings-tested and income tested
-some of the savings-tested supports exempt savings that are in government registered savings accounts (e.g. Registered Disability Savings Account) or disability trusts (i.e., accounts that dictate/restrict how the savings are used)
-most programs allow a person to work while receiving, but some deduct all additional sources of income (work income, child support, etc) dollar-for-dollar from the support, some allow a buffer (e.g., keep the first $500/mo, rest is deducted), some allow the recipient to keep up to $5000 per year in work income and all amounts from any other source, etc
So, depending on the type of support and the tests implemented, a person may have
-enough to pay not even their basic bills,
-enough for basic bills,
-enough for basic bills and a cushion, or
-enough for bills, a cushion, plus some left over to invest.
In our case, we have been in all of the above positions, depending on how much I can supplement the budget via work. For stretches of up to 12 years we received no income-tested support -at points because work income was sufficient to disqualify us, at other points because the systems were too difficult for me to navigate while parenting a child with disabilities.
In this order, I put the money primarily into:
-essentials (rent, minimal phone option, etc)
-child's therapies and child's legal care
-long term disability savings accounts for child
Folks qualifying for benefits need to look at their entire circumstances, plus the full range of supports offered and the specific terms and conditions of each, before they can assess what might be a fit.