Aviation is not set in stones and is not always black or white.
Are you departing out of an airport with high terrain surrounding you like Salzburg? I would definitely be taking the gear up. Is it out of an airport with no terrain? Then you could consider to leave it out, but if you do leave it out, you probably wont have fuel to reach your destination - as the 737 FCTM suggest you should/could continue to in order to plan ahead and reduce weight - and thereby already limiting your options.
Weather wise, VMC vs IMC and other things springs also to mind - but generally I would take the gear up as FCTM suggest, only time where I would consider not to do it is with an indication of wheel well fire and keep the gear out.