No it is not necessary. I haven't belled the mouths on any cartridges in a good 30 years, and I have never crushed a case, or other wise had a problem since. As you stated, as long as you ream and chamfer the mouths, jacketed bullets slide right in without any issues.
If the mouths are lightly prepped with a ream and chamfer the bullets will set up straight on the mouth, start straight, and seat with full neck tension and eliminate the need for crimp to close the belling. And if you consider the decrease in working of the brass, brass life does increase a bit as well.