It could be used for that purpose, but I think the original idea was so that a soldier in the field could use the rim of a cartridge to re-cock the rifle, without opening the bolt, as mentioned above.
During the time period the Mauser first came into use, case head failure, hang fires, and misfires were common, at least with the .30-06 military ammunition.
The same situation probably existed with forign ammunition as well, so a method was devised to re-cock the firing to try again before the action was opened.
By designing the slot so that a cartridge case could be used, a tool to recock the rifle was always readily available to a soldier in the field.
I have never had a problem disassembling a 98 bolt by placing the wing safety in the upright position. Of course, if it has been modified for a side safety, then the slot would be handy as you describe.
My rifle built on an FN commercial action has a small hole in the sear, and a small finishing nail fits to hold the cocking piece back to take the firing pin out. But, it also has the slot, if needed.
