i guess it comes down to... are secretions a problem now, or is potential atelectasis/collapse the bigger problem

if someone doesn't have lots of secretions now, or difficulty clearing, then manual techniques are useless and should be avoided.

if they do have secretion problems, are we doing everything else possible before resorting to manual techniques: mobilising the patient if possible (walking or ex bike), position, humidification/nebs, getting them doing adequate deep breathing themselves etc