How does a pair off fee work?

I'm curious about how a pair-off fee works in the world of cryptocurrency trading. Could you please explain in simple terms what it entails? Does it apply to all trades, or only specific ones? And how does it impact the overall cost of trading for investors? Additionally, are there any strategies or tips that traders can employ to minimize the impact of pair-off fees on their portfolios? I'm eager to gain a deeper understanding of this aspect of cryptocurrency trading.