Excel template -Value showing decimal

hi ,

I am trying to load data from an excel file to Oracle table.
When I click "get field from header row ..." , it shows few columns as number and few as string.
After this when I click "preview rows" then it shows value with decimal i.e 2345.0 for 2345 for columns with data type number.

When I put "#" in format for the same column I can see the value as 2345.

So I am trying to understand , how "#" help us here i.e. what happens internally.