I read once that the more a problem has some symmetries the "easier" it is to solve and in particular its (time) complexity is polynomial.
Conversely, when starting from a polynomial problem, if you break its symmetries, as an example by adding constraints, its complexity soon becomes exponential or at least no more in P.
Do you know some examples of this ? I wonder also if I could find a more thorough description, for any kind of problem, of the relationship between its symmetries and its complexity ?