In accidents where the other driver is at-fault, claimants almost always have two claims: a property damage claim and a personal injury claim.
The property damage claim is generally fairly straightforward. Either your vehicle sustained repairable damage and the insurance company will pay for the repairs to your vehicle or they will pay for the value of your vehicle because your vehicle is a total loss. Deriving the repair costs or the value of a vehicle is fairly easy as there are many benchmarks that our society and community have come to accept and rely on, including reputable body shops, Kelley Blue Book, NADA Guides, and other fair market valuations/tools.
However, the personal injury claim is always much more complicated and complex because there are many factors that must be evaluated and considered. An injured party is entitled to be compensated for: medical bills that they incurred, the wages they lost, loss of consortium or loss of services with a spouse, loss of enjoyment of life, physical/mental pain and suffering, disfigurement, and permanent injuries.
Insurance companies, because they are businesses and their objective is maximize profit, want to place as little value as possible on these factors in order to pay you as little as possible.