If you want to normalize all columns the same way (i.e., using the median and inter-quartile range of the entire data set), then use "all".
If you want to normalize each column separately (i.e., using each column's own median and inter-quartile range), then do not use "all". And in this case, it's best to use the dim argument set to 1, to explicitly say you want the median and iqr by column, in order to properly handle the situation that your data set has only one row.
