Code inspection pays for itself during development, isolates defects much more efficiently than testing, and has been shown to reduce maintenance costs by 90%

Research into Code Inspection
Why should you inspect software?
Immediate Return on Investment

Code inspection pays for itself during development, isolates defects much more efficiently than testing, and has been shown to reduce maintenance costs by 90%.

Research has yielded these findings:

Quality processes reduce errors without increasing costs. Increased quality assurance is associated with a decreased error rate but does not increase overall development cost.
Inspections cut rework by half. Raytheon reduced its cost of rework from about 40% of total project cost to 20% through an initiative that focused on inspections.
Inspected software costs 90% less to maintain. ICI found that maintaining a portfolio of about 400 programs was only about 10% of the cost of maintaining a similar set of programs that had not been inspected.
Inspection catches 70% of defects. The combination of design and code inspections usually removes at least 70% of the defects in a product.
Inspection catches 60% more errors than testing. Code inspection at NASA's Software Engineering Laboratory found 20 to 60 percent more errors than testing did.
85% of errors are trivial. About 85% of errors can be fixed in a few hours.

Research into Code Inspection Why should you inspect software? Immediate Return on Investment

Research into Code Inspection
Why should you inspect software?
Immediate Return on Investment