For the last couple of years, CFIs I've flown with (instrument, commercial and IFR currency flights) seem to have the same response when I announce that I'm going to cross at midfield to join the left downwind. Without fail they proclaim some variant of "it's probably better to just join a regular crosswind instead of midfield". When I press them about why, they usually say "it's just a better practice" or they really don't know why but it's what they were taught. To me this makes no sense at all. It would seem clearly better to cross at midfield where departing traffic is less likely to be climbing through my altitude. Flying a regular crosswind puts me right in the path of departing traffic. Are they worried about landing traffic making a go around? I would appreciate thoughts from all but especially CFIs that hold this opinion.