Use both for best effect.
An example:
Drum sound on a couple of trigs, pattern looping.
Playback page:
Turn up the RTRG amount to between 2 and 16 for example.
Turn up RTIM until you have some extra drum hits playing between your trigs. Not buzzing but playing the whole sample.
You may want to play with hold and rel times on the amp page depending on the sound.
LFO:
Trig set to ONE
Parameter VOL
Turn down the VOL on the amp page to give room for the LFO to work.
Waveform can be ISAW or EXP (experiment with others too)
Adjust multi, speed, and depth until you hear the re-trigs fading out in volume (like a delay tail)
The “ONE” setting will make it so that only the original real trig will trigger the LFO once. The volume will fade out on the retrigs (with the right speed and depth settings) until another “real” trig happens.
You can then set another LFO to PAN to make a sort of ping pong or stereo type delay.