Interesting thing though... when you CAST/CONVERT to INT, CHAR(160) will raise an error. But if you try CAST/CONVERT to FLOAT, statement will succeed and the nbsp character is ignored, if it is at the beginning of string (not if it is on the right end of string).

select cast(char(160)+'1234' as float)

select convert(float, char(160)+'1234')

Probably, as Jeff said, it is ignored if used to pad the numbers from left. Well... At the same time, select ISNUMERIC(char(160) + '1234') returns 0. As mentioned already several times, ISNUMERIC is rather unpredictable and should be avoided or used with great care : some strings that return ISNUMERIC = 0 can be successfully converted to float.