We have purchased property with section 8 tenants in place, and have rented existing property to section 8 tenants.
A fair amount may depend on where you are and who manages section 8.
Not everyone on public housing assistance is in section 8, sometimes I wonder if some of the negative views on "section 8" are actually toward other programs. At least in the areas I am familiar with (CT, upstate NY), if the section 8 client 'messes up' in any way, they are in danger of being dropped from the program. And in CT there was a very long list to get approved, so section 8 clients tended to be pretty good.
The two biggest things to be aware of in our experience are annual inspections (in an older building, something that has been fine in their eyes for years may suddenly become a "fix or be sanctioned" issue - e.g. surprise, all carpet must be replaced now) and some tenants not being able to pay when their portion of the rent increases dramatically. In most areas, if you do not wish to make the improvements that is an option *before* the tenant moves in; with a continuing tenant, you can still make that choice but depending on policy & timing you may be out the non-tenant paid portion of the rent until the tenant vacates.
Aside: if there are children in the unit, section 8 inspectors tend to be especially vigilant re: peeling paint (if the building is old enough to possibly have lead paint - inside *or* out). This isn't a problem really, kids shouldn't be exposed to lead, but if you are buying a building you might want to have that in mind when you make your own inspection.