Depends on preference, training, habit, comfort, playing style, size of hands and instrument, etc. When I use fingerpicks on steel-string small lutes (mandolin, tiple, cuatro-menor) or a flatpick I do not anchor a pinky. When I pick with bare fingers, whether on steel or composite strings, I tend to anchor -- unless I feel like picking down the neck or against the bridge. I feel more need to anchor when playing smaller 'ukes without straps than with the tiple or baritone and their straps. And fingerpicking chords allows more leeway than picking melodic lines which DO need the stability. Anchor for precision; flop around for freedom.