A complete brake job should restore the vehicle's brake system and braking performance to good-as-new condition. Anything less would be an incomplete brake job.
Brake components that should be replaced will obviously depend upon the age, mileage and wear. There is no pat answer as to which items need replacing and which ones don't. It's a judgement call.
A complete brake job should begin with a thorough inspection of the entire brake system; lining condition, rotors and drums, calipers and wheel cylinders, brake hardware, hoses, lines, and master cylinder.
Any hoses that are found to be age cracked, chaffed, swollen, or leaking must be replaced. Make sure the replacement hose has the same type of end fittings (double-flared or ISO) as the original. Don't intermix fitting types.
Steel lines that are leaking, kinked, badly corroded, or damaged must also be replaced. For steel brake lines, use only approved steel tubing with double-flared or ISO flare ends.
A leaking caliper or wheel cylinder needs to be rebuilt or replaced. The same applies to a caliper that is frozen (look for uneven pad wear), damaged or badly corroded.
Leaks at the master cylinder or a brake pedal that gradually sinks to the floor tells you that the master cylinder needs replacing.
The rotors and drums need to be inspected for wear, heat cracks, warpage, or other damage. Unless they are in perfect condition, they should always be resurfaced before new linings are installed. If worn too thin, replace them.
Rust, heat, and age have a detrimental effect on many hardware components. It's a good idea to replace some of these parts when the brakes are relined. On disc brakes, new mounting pins and bushings are recommended for floating-style calipers. High temperature synthetic or silicone brake grease (never ordinary chassis grease) should be used to lubricate caliper pins and caliper contact points.
On drum brakes. shoe retaining clips and return springs should be replaced. Self-adjusters should be replaced if they are corroded or frozen. Use brake grease to lubricate self-adjusters and raised points on brake backing plates where shoes make contact.
Wheel bearings should be part of a complete brake job on most rear-wheel drive vehicles and some front-wheel drive cars. Unless bearings are sealed, they need to be cleaned, inspected, repacked with wheel bearing grease (new grease seals are a must), and properly adjusted.
As a rule, tapered roller bearings are not preloaded. Finger tight is usually recommended. Ball wheel bearings usually require preloading.
As a final step, old brake fluid should always be replaced with fresh fluid.