It's not just a possible danger to the shooter, but possible damage to the rifle. Pierced primers can lead to firing pin or bolt face erosion.
How fast will it occur? I don't believe there is a good answer to that.
It depends on whether you want that particular rifle to last. If it's a "truck gun", perhaps there is little cause for concern.
On the other hand, if it is a custom varmint rifle, I would not want to have to replace the bolt...
.30-06 Springfield: 100 yrs + and still going strong