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Commas are an exception to that. If you paste in "10,100", it will be interpreted as a number, and you lose the comma.

If you enter a string whose first character is a "0" and Excel decides to change it to a number, the "0" is lost.

Once the data is in the cell, changing cell formatting is a nondestructive visual layer. But while inputting data, cell formatting changes the interpretation of the input, which is destructive.

The article describes in some detail how inputting SEPT2 in a cell with default formatting displays 9/2/2016, but is stored as 42615 (which you get if you later change the cell to text formatting).