A Rake Receiver is a useful way to mitigate the effects of multi-path fading caused by selective channels. you have to use it with CDMA due to the orthogonality of the signals over a period reciprocal of its bandwidth. if you do not use a rake receiver with cdma you may face internal noise generated due to lack of orthogonality and that would decrease your performance.
in case of OFDM, rake receiver is not used. because it uses multi-carriers each delivering low bit rate. rake receiver is useful when using a single carrier signal delivering high bit rate like the case of cdma or w-cdma.