Is Dry Cabinet better or a Dry Box? and is it necessary for (a) A Point and Shoot Camera (b) a DSLR Camera?
Not usually but it probably depends on where you live.
The maximum storage humidity of cameras is relatively high but I do take extra caution while in tropical rain forests which I'm kind of far from right now. I own several cameras and dozens of lenses, some of them do not get use for months and even years at a time and never had any problem despite the climate changing here significantly and get quite humid.
For long term storage, I keep the cameras in their original cardboard boxes with silica pouches. They change colors when too humid and all you need it to but them in a dry frying pan for a few minutes to get them back to normal.