See batteryuniversity.com for the study he did about depth of discharge versus battery life.
The distribution is rather wide so getting persnickity about 50.0% isn't necessary - it is just a good guide. Note also that float service, which is keeping the battery from going down more than 10% or so, is also not good for the battery.
On a campout, it is easy to check voltage but do so only after the battery hasn't been doing much for a half hour or more. If the voltage starts to get below 12.2v then you need to start thinking about charging. If it gets down to 12.0v, the charging needs to become a priority.
see Basic battery guidelines