We currently use a DEFAULT_FLOAT_PRECISION of 5 in cqlsh with formatting '%.*g' % (float_precision, val). In practice, this is way too low. For example, 12345.5 will show up as 123456. Since the float precision is used for cqlsh's COPY TO, it's particularly important that we maintain as much precision as is practical by default.
There are some other tricky considerations, though. If the precision is too high, python will do something like this:
That's not terrible, but it would be nice to avoid if we can.