I don't hunt bears much but I'm like Yukon Jack, it depends for me. Since my 300 win rifle only holds 3 in the mag, I often chamber a 4th - ESPECIALLY IN THICK BEAR COUNTRY. In the tent at night too. But I often hunt alone. In the boat, on the snogo, or around camp during the day, or when others are around I try to keep the chamber empty.
A retired school teacher nearly blew his arm off a few years ago when his slinged 375 H&H tangled with the caribou rack he was packing. Knowing the guy and talking to him about it has made me more careful about carrying with a chambered round. Cell phones, air abulances, some good EMTs, and the wonders of modern medicine saved his arm- but I sure don't want to go through that or worse.