We have all done it before. When something important falls into your inbox, you already know who you're going to hand it to. The person who does it the way you want, on time, without you having to check in twice. Going to them makes sense. But it can also be the start of a problem if you make this a habit.
This is how it starts. There's less friction all around by going to your strongest person. The request is easier to make, because you don't have to explain it three times. What comes back is reliable, because they know what needs to be done. So you go to them again, and then again, not out of laziness but because it works.
Even though it works, the cost is hidden. Every time you route any task to the same person, you are withdrawing goodwill from the bank. Spend that on ordinary work or non-critical tasks and you risk running the account into the negative. That leaves you zero funds for when you really need them.
I am not saying you shouldn't lean on your strong performers. You have to, especially when something really matters. The problem is leaning on them for everything. Being reliable is the thing that makes them valuable to you, and steady withdrawals from the "bank" will run the account dry.
Be deliberate about what you hand them. Not every task needs your most reliable person. A lot of the work is routine, and routine work is what should be spread across the team, including the people still finding their feet. Save your strongest person for the things that actually call for them. Decide it task by task, on purpose, instead of defaulting to whoever is easiest to ask.
This is separate from a stretch assignment you give someone to grow them. That kind of load is deliberate, and it belongs to development. What I'm describing is the accidental version, where one person absorbs more and more because asking them takes the least effort from you.
Here is why a habit of always going to the same person is a danger. Your best people usually won't tell you they're underwater. They take the extra work, get it done, and say nothing, because being the one who can handle it is part of how they see themselves. The overload stays invisible to you right up until something breaks.
The rest of the team sees it before you do. As a manager, some things are just harder to spot right away, but the team sees everything. They watch one person carry more than everyone else, and while nobody raises it in a meeting, it settles in. The person doing the extra work can start to resent it. And everyone else quietly learns that this is the normal routine. Those are the problems that you will never hear. If you're not paying attention, your most capable person burns out, or worse, starts looking for an exit.
You need to pay attention closely to how you are delegating. Look at how many of the last handful of urgent tasks actually went to your go-to person, and how many of those could have gone to someone else. The number will tell you more than what your gut does. Keep notes and make it simple, but keep track to see how you are balancing the load.
Leaning on your best person feels like good management. Overusing them is how you drain their account. When you protect their capacity, you are protecting the exact thing you were counting on.