Maybe older versions of plex did it?
I am running my PMS on my 'server' box. Quad core 3.0 AMD, 8g ram.
Idle (with whatever was just running on the server), was at 13% cpu and 3g of ram used.
Streaming a 1080p video, 5.1 sound (obviously the apple is not using that, but its what its encoded in).
Cpu only ever went up to 16%. Memory up to about 3.6g
So it may be dependent on what hardware your running PMS on..
As well, how/what your outputting. Generally for the iOS devices.. I have found NO NEED for transcoding. Transcoding would take up MUCH more CPU usage.
My Samsung TV, has an issue with the encoded subtitles on the anime I watch in MKV containers running as just a stream. (everything else streams fine).
Those I do need to turn transcoding on. I would have to see what the usage jumps up to.
But myself have never had really an issue with FF/RW... but again, maybe the difference of transcoding/not effecting it.
Rogers Ignite Xi6, LG 47LV5400 LED TV, Yamaha