"You should never remove code that you don't understand."
Never is a long time.
It's fairly easy for low-skill developers to write code that's time-consuming for high-skill developers to understand. In fact, making simple things hard to understand is pretty much the definition of bad code.
So, you use your judgement. If it's a particularly subtle and important part of the code, spend the extra time to make sure you're not missing anything. If it's not, then just rip it out and don't waste time in a maze of strange control flow, redundant code, useless invariants, and confusing assumptions.
Never is a long time.
It's fairly easy for low-skill developers to write code that's time-consuming for high-skill developers to understand. In fact, making simple things hard to understand is pretty much the definition of bad code.
So, you use your judgement. If it's a particularly subtle and important part of the code, spend the extra time to make sure you're not missing anything. If it's not, then just rip it out and don't waste time in a maze of strange control flow, redundant code, useless invariants, and confusing assumptions.