Darrell Thorp explains why he puts his lead singer on a U47 and the backing vocalists on 67s instead of using the same mic for everything. The tonal difference between the two mics gives each part its own texture, so the lead sits loud and clear while the BVs sit distinctly underneath without a separate EQ move.
His take: if you have two great mics you love singing on, dedicate one to leads and one to backing vocals. The contrast in timbre does a lot of the separation work before you even touch a fader.
Thorp also shares a story about a singer who used four different mics (a 47, 67, 49, and C37), switching between them for the lead, the double, and alternating takes. Each mic change gave that part its own character, adding subtle variety across the vocal stack.