For weaker or thin-sounding tones/instruments, I layer a 2nd tone that compliments the lead tone, and save this as a registration.

There are so many tone-shaping parameters available, delays, attack, chorus, flanging, echoes, reverbs, spatial, etc, etc.

For example, on a 12-string guitar, I might set the 2nd tone to be the jazz guitar with the attack or harmonic content set low, reverb up a bit, and slight chorus added. It helps fill or sustain the 12 string sound in parts of a song where the notes are held out for longer periods (half, whole notes).

On a preset organ tone that I liked but wanted to have more 'punch', I adde a 2nd organ but it sounded muddy, so I added an electric piano, cut back on the chorus, brightness and harmonic content parameters and that gave me the punch without the piano hammer-striking sound.

So many parameters and variations are there to pretty much mimic any tone you want.

I usually hear layering used to add other instruments to the delivered sound, to increase the size of the band, like strings with piano, the sax section with the brass section, but for lead/solo sounds, layering 2 or more tones that harmonically compliment each other works great.