When does it make sense to file a demand for international preliminary examination?

Generally speaking, it makes sense to file a demand for international preliminary examination under PCT Chapter II only if you received a "negative" international search report (ISR) and written opinion (WO-ISA) but you believe you can file amendments and/or arguments during the proceedings which could lead to a "positive" international preliminary examination report. In other words, an international preliminary examination gives you the opportunity to respond to any negative finding of the EPO acting as ISA while you are still in the centralised international phase under the PCT, which saves you from later having to draft and file multiple responses with the national/regional offices upon entry into their national/regional phases.

In addition, you will benefit from a 75% reduction in the examination fee in the European phase if the EPO has already acted as IPEA.

However, if the EPO acting as ISA has issued you with a declaration under Article 17(2) PCT that no ISR has been established ("declaration of no search"), filing a demand is not recommended, since the EPO as IPEA will not examine claims for which no ISR has been established.