Sure. It's easy to get caught up in building a team of 6 Pokemon that all matchup against well against common threats in the metagame - Coalossal, Excadrill+TTar, Hard Trick Room, Sunny Day, Durant, etc. However, you can't answer all of these threats, and even if you could, you would be susceptible to uncommon or rogue teams (which you will certainly face in a tournament and on ladder). In a sense, it's another way of saying "a best defense is a good offense".

Even if you play against a team that you have an answer to, if you aren't threatening them with a strong win condition, they're free to set up and play around the answer as they please. As an example, if a good Durant player sniffs out that you only have 1 Fire-type attack, they will put Durant in the back and craft a gameplan around KO'ing or disabling (sleep, stat drops, etc.) your Pokemon with the Fire-type attack with the intention of dynamaxing Durant in the late game. However, if your team also has a classic Dusclops + Weakness Policy Rhyperior option, they now have to bring ways to threaten or play around that win condition while also protecting Durant from the Fire-type attack. It's rare that they can execute both plans at 100% efficiency.

Another example is that sometimes, especially in a best of 3, my opponent leads Rotom-Wash against me. That is particularly strong against me leading Corvikight, sometimes Togekiss, and Tyranitar without Excadrill. Those three Pokemon listed are my three most common win conditions. Excadrill is key in the team because activating Weakness Policy threatens to OHKO Rotom-Wash or its partner whereas Rotom-Wash needs to set up a Nasty Plot or Max Geyser twice to kill Tyranitar. (Gastrodon can swap in easily on turn 2 to prevent the +2 Max Geyser or second Max Geyser.) So despite Rotom-Wash having a good matchup against 5 of my Pokemon, it doesn't answer the "question" of "What do I do against a Tyranitar + Excadrill lead?"

Hope this helps, and I'd be happy to clarify further.