Personally I prefer weighing and use that for the majority of items, but there are some thing that don't make sense to weigh and will be less affected by how tightly I pack the cup, like when I make soup. When I make something like that, I measure yield (in cups), figure out the stats for per cup or whatever, and then use that for recording amounts.
Ounces by volume can be very different than by weight because food doesn't weigh the same, even if it seems like it would. I'm a beekeeper, and we have to sell honey by weight, because 8 fluid oz (by volume) of honey weighs more than 8 oz by weight since it is so dense. It can also vary from honey to honey depending on moisture content, etc, so weight is more variable.