It never hurts, though it’s more important with some knots than others. As a general rule, anytime you tie a knot that gets its strength from a series of wraps or coils that cinch down very tightly, adding a little saliva is a plus. This is especially true when tying these knots with monofilament or fluorocarbon. Heavy-gauge mono and fluoro will create more friction during the tightening process than light mono and fluoro, making lubrication even more critical. Although many of these knots require a little abrasion within the coils to maintain strength, too much is a bad thing. It’s always smart to wet an improved clinch or uni knot before tightening, and if the idea of using spit grosses you out, hit the wraps with a little lip balm instead.