Let's look at what the adcom sees when you complete the AMCAS:
Your employment during college including number of hours worked per week
The number of credit hours per semester you took
Your parents' the county where they live, most recent school attended, highest educational attainment, and their current job
Your permanent address
The place where you were born
So, without claiming disadvantage, an adcom can know that (for example) your mom never finished high school, that your dad attended junior college but didn't graduate, and they live in a rural (or urban) county where you were born. They can see that you immigrated or that you were born here but that they went to school abroad. They see what kind of employment your parents do (or that they are unemployed, disabled, retired, or deceased). They can know that you worked 3 jobs for a total of 40 hours per week while taking 15-16 credits per semester.
Now, if on top of all that,
if you think that you were economically deprived during childhood (before college) because your family had a low income, received federal aid (e.g. welfare, medicaid, food stamps, free school lunch), that you worked during H.S., that you did /didn't contribute your wages to the household expenses then you can provide additional information on the AMCAS about that disadvantage.
In some cases the disadvantaged thing sheds some light on the family circumstances (parent with high education but mental illness that precluded working thus resulting in a very low family income and minimal support at home). Used wisely it can be helpful to the applicant but if one sounds like

it could hurt anotherwise acceptable applicant.