What does 'round up to minimum trade size' mean ?

If no minimum lot size is set by the broker, all trades will be opened at 0.01 lots when calculated lot size is below 0.01, even if this option is not enabled.

However, if a minimum lot size is specifically set (e.g. US100 with a minimum of 0.1 lots), and the copier's calculated lot size is the below that minmum. Then if round up option is not enabled, the trade is missed but if it is enabled then the lot size will be rounded up to the broker's minimum (e.g. 0.1 lots) and the trade will be placed. This means that all trades will be opened even if the calculated copy size is less than the minimum trade size the broker has available.