The main significance of the case of Oregon v. Rideout is that it helped to make prosecutors leery of trying men for raping their wives. The case did not set any new legal precedents. Instead, it simply illustrated to prosecutors how difficult it would be to convict a man of raping his wife.
Rideout was tried in 1978. At that time, the state of Oregon had very recently changed its rape laws to say that it was possible for a man to rape his wife. The rape laws in most states still stipulated that a man could only rape someone who was not his wife. The idea was that a woman consents to have sex with her husband when they are married and that consent cannot be withdrawn. Since then, all 50 states have changed their laws to some degree. It is at least possible for a man to be charged with raping his wife in every state today.
The importance of Rideout is that it helped to show that prosecuting this crime would be very difficult. In this case, the husband was acquitted of raping his wife. This was largely because the jury could not find that the sex had been nonconsensual beyond a reasonable doubt. To this day, prosecutors tend to be wary of trying to take marital rape cases to trial. This is, in part, due to the legacy of Rideout.