Advantage of complex filtering in multirate applications I've seen it mentioned in passing in various papers on signal processing and filter design that complex FOR filters can be more efficient when it comes to multirate applications. However I cannot think of a scenario where this is applies. Of the systems I've seen, the baseband is complex which means generally the baseband for interpolation (for example) filters makes most sense with real coefficients so +ve and -ve frequencies are both passed.

Can anyone give examples where a complex bandpass filter makes sense, and specifically to areas like decimation and interpolation.
For one practical example, I'll point to GNURadio's frequency translating FIR filter block: https://github.com/gnuradio/gnuradio/blob/master/gr-filter/lib/freq_xlating_fir_filter_XXX_impl.cc.t

It's a channelizer  &amp; decimator block that gains an efficiency by spinning a user provided FIR LPF up to be a complex BPF where the channel is and filtering first vs. spinning the channel down first.  The efficiency comes from performing the frequency rotation at the lower sample rate after filtering and decimation vs. before.