I'm quite happy to say, that mortars in FOW are very useful to any infantry list.
It's ability to smoke or pinned infantry outweigh its capability to kill.
Unlike the worthless mortar of my Warhammer 40K days (it sucks in Imperial Guards, can't kill for nuts...)
FOW mortars plays an integral part of an infantry list in either supporting for an assault or blinding long range guns.
In my tournament list, I am playing a Fallschirmjager mortar platoon (2 x 81mm mortar sections) and attached HQ mortars ( 2 x 81mm mortars) to support my infantry marching across No Man's land.
It will be useful as well to blind any arty observers if needed be.
Note that the Fallschirmjagers used an airborne version of the standard 81mm mortar which they nicknamed it as "stumpy".
For those serious wargamers who are into the nitty gritty details of mortars used by the Germans, I have found an interesting link to read up about the use of 8cm Granatwerfer 34
8cm Granatwerfer 34
8cm Granatwerfer42 Stummelwerfer