In previous company (NG"s) always surprised me an otherwise good to excellent Bad WX Ops pamphlet had this flap exercise after pushback because:
- having just de-iced and anti-iced the wings/slats and gaps etc will be as clean as they can get;
- exercising if precipitation/snowing means allowing ice into the flap gaps to be crunched after retraction and freeze further even more on taxi out.
My procedure was to not do the check after pushback and taxi out flaps up, just before take-off exercise to 40 degrees, back to 5 degree (only company setting) and if all OK take off; any problems taxi back for de-icing etc.
Discussed with a checkie type who only smiled and said "as long as it is done somewhere at PIC discretion is OK", management did not want to buy into any talk about (maybe IMHO) changing the location for the check - so some crews would be stuck with "the C/L says MUST be done after pushback" mentality which didn't appear the best/safest option.
Cheers.