I think the idea behind analyzing with symmetry is to reduce the analysis time by using only a portion of the model. If done correctly the results should be applicable to the entire model.
To start out - you might do some tests using symmetry and then the entire model to see how the data comes out. (be sure to measure the time to achieve the results and the check the results themselves for each method).
Thanks for your help
what is your concern regarding symmetry? it might be easier to ask if we know the background for your question. are you getting bad results or do you have a concern about the BC?
all that a symmetry BC is saying is that at the cut, there are no rotations at the plane and no motion perpendicular to the plane. thats what would happen at a cut face in the middle of your part in real life. it doesn't care about the geometry size as long as it is right in the middle.