Range in Remove duplicates

I have a block consisting of 25 columns, 500-600 rows and a unique identifier in Col A. Sometimes I need to remove duplicates and I have tried this, but it does'nt work:

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so instead I have this line:

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and it works regardless of what I have put in as Range as long as it is a single cell in the worksheet.

What is the purpose of defining the Range?

NSV

PS: If someone can tip me with a more elegant way of defining the number rows, I'd appreciate it.