Obviously you have more control with hand cast gels - you can try a higher acrylamide % in the same day if you want to. Precast gels also expire and don't work well close to expiry in my experience, so there is potential wastage and a higher cost. I can see the advantages of precast gels if you are doing a lot of western blotting for publication figures, but if I was just checking the purity of a protein prep via coomassie stain and only needed 2 lanes using a precast feels like a waste.

Always use precast gels if possible,(e.g. Novex), saves a lot of time, quality is great.

Shelf life is much longer than expiry date and if you don`t have a specific purpose,

you can buy 4-12% gradient gels.

I prefer to use pre-cast gel if: a) I have very few samples to run b) I need to get results quickly, or c) I need to use specialized gel to separate proteins (i,e. gradient gel) rather than regular stacking-resolving gel set-up.  In my opinion, pre-cast gels give more consistent results than hand-cast gels.  Also, you can buy what you need and use them up without worrying about making and keeping stock of polyacrylamide solution (I do not like to keep them around, but it is just my preference...).