The problem with cross-chaining is that
1. there's more force on one side of the chain than the other, which increases the chance of you breaking the chain...though most likely you won't be putting down a lot of torque if you're in such a combination
2. you're also pulling the teeth (on the cogs) at an angle, which causes more wear and chances of bending the teeth...but as stated in #1, you probably aren't putting a lot of torque in such a gear combo.