I think a strong imagination is probably one of the most useful things you can have in magic, because you use it in almost everything.
Visualization is part of it but imagination is more than seeing a picture in your head. For example you don’t just imagine a fire, you try to feel its heat, hear it crackling and maybe even smell the smoke. You create the whole experience within your mind and hold it there without it changing.
You need this for pathworking, invocation, energy work, charging sigils and many other rituals. It also trains concentration and control over your own thoughts. If you try to imagine a red triangle and it keeps changing its colour or shape by itself, you quickly realize how difficult real thought control actually is.
So the benefit is being able to direct your imagination through your will. The stronger this ability becomes, the more intense and real your magical work can become. You can perform all the outer parts of a ritual perfectly, but without imagination, internally there probably won’t be much happening.