Do you think just because people are married they don't need to use protection? I guess if you want to have a bunch of kids, you can go without, or if you want to be on the pill... some people don't like being on medications though, and for some people, the pill is not an option because of the medical complications it can cause. And, being married does not mean that both partners are faithful and will never get an STD.
Obviously assuming they are on the pill.
If you aren't on anything then yea use it.
And I don't think you need to put a tracking device on most guys to make sure they are being faithful..