Buying insurance salvage cars is generally not worth it for the average buyer because the quality of the car is uncertain. Some people with enough mechanical knowledge to assess their safety may find them valuable as commuter cars or in other limited situations, but it is risky.
In addition to the risk of mechanical issues, even fixed-up salvage cars in good condition generally have a very low resale value. They can also be difficult to find a buyer for at all, especially since most banks are unwilling to finance them. Some insurers are also unwilling to cover them because they are worried about safety issues. Professional rebuilders may cut corners on safety equipment such as airbags.