It will be recalled (see my blog post of February 2, 2018) that the search fee for ISA/KR will increase by about 7% for filers in RO/US. The increase will happen on April 1, 2018.
This offers an opportunity to save some money on PCT filing fees. A US filer who is considering filing a PCT application (and who plans to pick ISA/KR) on or after April 1 might want to consider filing it on or before March 31. This would permit the filer to pay the cheaper search fee.