The Use Doubles option tells Stat/Transfer whether or not to put variables with fractional parts into 'double' or 'float' on output. The default is now to have Stat/Transfer use doubles.
If you do not change the default behavior, Stat/Transfer will evaluate each variable to see if it can be represented as a 'float' without a loss of information and will put only those variables that require it into a 'double'. This is the safest option and is now the default.
However, most data are not measured with more than eight or nine digits of precision (survey data, for example, never are). Therefore, if you need to save space on output and do not need more precision, you can change the default behavior, so that only 'floats' are used.
You can reset the Use Doubles option by clicking on the Options tab, selecting General Options and uncheck the Use Double box.
Alternatively, for a single transfer, you can uncheck the Use Double box at the bottom right of the Variables dialog box and then press the Optimize button.