Wow, I can't tell if Meera was saying yes to use them or no to not use them...
But yes, you should use required deployment contexts when needed. Required deployment context has nothing to do with dependency management, it has to do with plugin startup management handled by the portal.
If plugin A is dependent upon plugin B, then Liferay will ensure that B is up and running before A starts. Dependency in this respect is dependency on runtime beans, not on compile time code.
It sounds like you're also mixing in the concept of the portal dependency jars. Here you still want to use this also, even under ant. At deployment time, Liferay will copy in it's own jars into your war file. The benefit of this is twofold - first you get the same version of the jar that Liferay is using (maximizing compatibility) while at the same time shrinking the size of your deployable war.
For each jar you list as a portal dependency jar you still need to add the dependency to the pom, but you use the "compile" scope so as to not include the jar in war build.
