[Patrick]

If a cell puffs up a bit you can see the case bulge as well, so it doesn't hide a bad cell.
I've seen one guy at racing accidentally leave his charger on nimh setting, then put a hard case orion pack on charge. When it puffed up a lot it just opened up the case, so it wasn't holding in any extra pressure. Luckily he saw the case split apart and took it off charge in time.
The case just protects from impacts and puncturing. I've seen a couple fall out cars while running on the track and they've been ok.