It's not whether or not to take time in Chopin (or any other composers according to musical style) it's HOW you take the time as naturally, organically, and convincingly as possible that matters most. Too many people screw around with music, justifying any interpretation because most composers were fond of unique renditions of their pieces. However, they were most likely uniquely good, uniquely logical, uniquely organic, rather than uniquely the opposite.
In terms of metronome markings, I'm from the opinion that realizes that composers have a tendency to compose their music, then place metronome markings that in more cases than not, are too fast. This seems to be because many composers haven't placed enough emphasis on the space that their notes require to sound. Read through a few chopin mazurkas (Op.17 No.4 comes to mind) to discover that some are just unnaturally fast. This also seems to be a prevailing trend in much french impressionistic music.