Several members of my local woodworking club believe that biscuits add no additional strength when gluing up most boards. They (and I) believe that they are helpful if you are gluing up boards that are oily and do not normally glue up well. They (and I) also believe that in certain situations the biscuits can aid in alignment. I will also add that I like to use them when gluing into end grain.
However, when making a table top by glueing up oak, walnut, cherry, etc. boards side to side, most of the woodworkers I know (including myself) no longer use biscuits.
How do others feel about biscuits?
-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.