THe joints would become loose in time ... or even worse, they would be loose out of the box. Then of course people would start clamouring for more joints, and the klicky would end up like one of these superhero action figures you see in comic stores: so many articulation points that it harms the actual sculpt. And what for ... for the figure to be able to bend over backwards and kiss it's own bottom? I can understand the functionality of a bendy elbow, but the rest ...
I mean ... what's the use of individually articulated legs? A can-can diorama?
I own several action figures that boast several points of articulation, and with modern materials I've noticed in most contemporary articulated toys, joints becoming loose doesn't seem to be a problem. however it might be a problem if playmobil continues to use the cheaper plastics they've been using for some of their more current clickies (or even the older plastic which was prone to joint wear and looseness).
practical-wise, assuming the joints aren't prone to looseness, actually, poseable clickies can be very practical, including being able to do a can-can diorama. I know, personally, I can appreciate the bending knees so that I can have two rows of firing redcoats: one in back, standing, and one in front, kneeling. And elbows would be awesome for many poses current clickes cannot do, including holding a rifle the proper way, for strafing the enemy, for holding a bow and arrow for archers to have better poses, for musician clickies to be able to not just hold their instruments at their sides, but be able to actually be posed PLAYING the instruments (violin, cello, guitar, saxaphone.) And even the pianist could do with some bending knees so he can sit properly at the piano and operate the foot pedals (instead of sitting with his legs straight forward up off the ground). The possibilities are endless!!!! These are just to name a few!