Depending on the vehicle, camber can have a major effect in cornering and handling capabilities.
Having the alignment set at a more negative camber will allow the suspension to roll during cornering, which makes the tire sit flat and have as much tread contact as possible on the road. Bit it will cause the inside to wear out faster than the rest of the tire.
Setting an alignment up for more of a neutral camber not necessarily give you more even tire wear because the suspension rolls a bit less, and the tire rolls a bit more on the outside shoulder, causing uneven wear.
It's been a while since I did alignments, and it really depends on the vehicle on how much is too much on negative camber. So I can't answer that question...