If you record at -6 dB, there are only 32,768 possible values to be assigned to your signal. You'll end up losing some of the dynamics. This will prevent ANY signal from exceeding the setting and distorting the tape. If there happens to be a loud peak, it will get compressed slightly before limiting, and it will sound a little more tolearble than the transition straight to hard limiting. Alesis ADAT's are sometimes known to eat tapes.
Some brands seem much better than others for longevity.
The hotter it gets, the more likely your tapes will get eaten. The rubber wheel in the machine doesn't grip as well, making the takeup reel lose tension when you start to play. Put a little space between your machines to let air flow between them. Rack fans help too. Don't enter transport commands quickly.