Do you mean the use of the electromagentic sprectum in treatment, or do you mean the use of magnets (sometimes electromagnets) in treatment which is often classed as an alternative therapy?
In the case of the former common examples are the use of x-rays to treat/destroy various types of cancers. X-rays being part of the electromagnetic spectrum. You could also have as an example infrared treatments for muscle strains. Then there is sun light to treat jaundice. To find impacts you could google these, there are wikipedia pages for each.
For the alternative therapys see here:
For part 2) PCR is a good example see: