Most obvious will be at 45 degrees the shadow of your subject will be much clearer and "more harsh" as compared to firing your flash at 60 degrees. Also from my personal experience, 45 usually caused over-exposure of certain areas of the face. It may be of my settings but I remembered reading somewhere it is advisable to tilt your flash at least 60degrees for human portrait shots.
However, do remember when your tilting, you are bouncing off flash light from the ceiling or whatever that is above you so watch the colour cast if boucing against non-white ceilings.
Just my 2 cents worth. Critics and disagreements are most welcome as I am here to learn as well. Cheers:cheers: