Assigning the result of querySelector to a variable with a specific DOM type, such as HTMLInputElement, is an important TypeScript practice. This approach allows you to safely access properties and methods that are unique to that element type. For instance, when you use HTMLInputElement, you can directly use properties like value and methods like focus() without TypeScript errors or the need for extra type checks. This type safety helps prevent bugs that can occur if you accidentally use a property or method that does not exist on the actual element. By specifying the exact element type, you make your code more robust and easier to maintain, as TypeScript will alert you if you try to use an invalid property or method for that type.