Club players have a tendency to open a strong 2C on many unsuitable hands. Experts tend to play 2C as 23- 25 flat or any strong and game forcing hand. The lower limit for 2C is a hand where partner might pass a one level opener but game is still likely. This hand, from the semifinal of the NEC Cup last year, shows what might go wrong. In two rooms, South opened 1D because there is no danger of the hand being passed out. The subsequent auctions in those rooms were like:
West has shown a two suited hand via a Michael’s cue bid and, when partner has shown enthusiastic support, West makes another bid over 5C.
North revalued the minor suit queens in one room and bid the diamond slam. In another room ( not shown), North passed 5H and South pushed again with 5NT and North again reached the slam. Both defenders tried to put East in for a club ruff. The 9S was a failure but a small heart was very successful!
In the other rooms, South decided to open a strong 2C and West took up as much space as possible without being too exposed to a large penalty. Rather than guessing to show diamonds, both Souths bid 4NT to show a two suiter. Now this bid might show both minors for you but there is no obvious reason for partner to choose diamonds rather than clubs.
In fact, for most experts, 4NT shows any strong two suiter and any suit response is passable and partner only bids again with the other two suits. Thus, North will bid 5S ( or perhaps 5NT) and South bids 6C in case partner has hearts and clubs! This contract, unlike 6D, is not safe and went four off for 15 imps out.
The lesson is clear, start describing your suits as soon as possible and avoid nebulous bids like 2C as much as possible.