|I think the answer to this really does just depend on your babe. For quite a while I did use a liner with every diaper, OS or L Sandys, on my DS#1, esp if I couldn't change him within about an hour and a half. Once he was about 20 months or so I didn't need the liner anymore because he cut back fluids. DS#2 has never needed an extra liner, except at night.
Both of my boys have been with AFs, not woolies; I'd wonder if possibly sitting (in a car or cart?) would compress the diaper/woolie and make it a little more prone to damp in that particular situation of heavy wetter with sitting?