It's depends on the context of your sentences and what are you trying to tell. The use of Kata Ganda is to show plural form of the noun. The usage in adverb somehow to stress on the object. It might sound similar in English but in Malay it gives some highlight. In general: kalau (jika, jikalau, seandainya) = if Kalau saya pergi ke Beijing esok, saya akan belikan kamu sebuah telefon bimbit. If I happens to be in Beijing tomorrow, I'll buy you a hand phone. kalau-kalau (mungkin, barangkali) = maybe etc. Pensyarah saya membincangkan senarai semak barangan keperluan perkhemahan esok bersama kami. Dia hanya risau kalau-kalau ada yang terlepas pandang. Our lecturer discuss the camping needs checklist for tomorrow with us. He just concern that maybe some stuff are overlooked. That's the example that I can think of.