The two items are not really related.
AllowUnsafeUpdates will allow changes to the content database happen on a GET request instead of a POST request. This is a very bad idea. It is very trivial to write a script to perform 1000s of GET requests per minute, which would update your content database with duplicates. The actual use cases for AllowUnSafeUpdates is very, very limited.
RWEP also has very limited use cases. The example in the previous answer is actually better solved by impersonating the system account. Use RWEP if you need to access non-SharePoint resources that are accessible by the application pool identity. If the resource is inside SharePoint, impersonating the system account will likely suffice.
In both impersonation and RWEP scenarios, you sould validate the form digest before performing any updates. Most responses on the internet omit this, advocating AllowUnsafe instead.