I use it whenever I can. If the tranny hunts, I turn it off. If the TC locks and unlocks, I take it out of what Ford call "Overdrive".
This is what both the Ford manual and the Internet guru of Ford transmissions, Mark K, over on RV.net, say to do and I believe them both.
2013 Starcraft 266RKS
1999 Ford E350 V10 Chateau (6.8L, 4.11 LS)
2005 Cedar Creek 31LBHS
2001 Sprinter 303BHS
1997 Mallard 33Z
1990 Starcraft Starmaster