Inspired by an answer to "Why does a run of 4 in Cribbage score only 4?".
The best possible hand in cribbage is 29, which involves the Jack that counts for nobs and all of the 5s. Now although hands with lots of fives are always good, often retaining just one or two will only result in a mediocre score where you count a few 15s, a pair, and are done.
For example if you're drawing for the best possible hand failing to get that last 5 as the up card will cost you 14 points, as you'll only score 15-8, a pair royal for 6 and 1 for his nobs for 15.
Note: I think the count given is a bit off, or assumes something not explicitly stated -
555J on its own, with the J not matching any of the 5s - scores 14. Four 15s (8), plus trips (6). So, any up-card that doesn't add to that score in any way costs you 15.
As stated above, the best possible hand in cribbage is an extremely rare case. It first requires a player to be set up with a hand that happens rarely on its own (
555J, all different suits). Then, it requires the up-card to be one specific card - the 5 matching the in-hand J.
Playing for this scenario, when dealt the proper hand, could be a very risky proposition. There's about 15 points of difference between the minimum and maximum possible values of this hand, depending on the up-card. Though the minimum score of 14 is still a fairly decent hand, there's many ways that the opponent could easily out-score this hand.
Additionally, keeping this hand sets the player up to have points pegged against him which might be more easily avoided with a different hand selection. If the player is forced to play a 5 when the count is zero, there's a very strong possibility their opponent has something to make 15 with.
Of course, the risk/reward scenario isn't just a matter of "I might score 14 or I might score 29". There's still a number of possibilities in between. So, what are the general odds that the final hand score might still be favorable? What possibilities exist between 14 and 29 here, and which are most likely?