While I had a minute, I did some “digging”
In his Exposition on the Apostles Creed, Thomas Aquinas asserts that the first and primary reason Christ descended into hell was to bear the whole punishment of sin, so that he might wholly expiate sin.”
Question: Christ’s descent into hell
http://www.newadvent.org/summa/4052.htm
One is what you said. The other is the so-called "harrowing" to which Peter alludes and about which there is a very fine description in the apocryphal Acts of Pilate.
I don't know much about it, but I have read that Hans Urs von Balthasar is thought by people who know more than I (a LARGE group) to be wrong in saying that in Hell IHS suffered the extreme alienation from God which is the ultimate effect of sin.
Personally I think that as IHS conquered death by suffering it, it is not so outrageous to think that He harrowed Hell by entering into it fully, so I see no conflict.