Denti,
Yes in the case when a ice run up is needed of course it MUST be done.
Apart fromthat case, Boeing clearly states that above 40 perc n1 and no fwd movement ,the engines start to ingest ground debris (especially with light crosswind)while the performance gained is closed to NIL.
CFM in its cold weather info advises to avoid thrust higher than 40perc or doing static run ups in areas where lose ice or snow accumulation are present.
Darius ,,you are dismissed.