The Nuance Difference: "たいてい" vs "役に立つ"

In Japanese, both たいてい and 役に立つ are often translated to English but have distinct usages. たいてい (たいてい (taitei)) represents "usually, mostly" (Level: N5) and typically represents Adverb of frequency. Indicates something happens most of the time, but not necessarily always. Stronger than 時々 but weaker than いつも.. On the other hand, 役に立つ (やくにたつ (yaku ni tatsu)) translates to "to be useful, to be helpful" (Level: N4) and is used for A set phrase meaning to be useful or helpful for someone or something. It describes the utility of an object, skill, or person. Often followed by the particle に. Mixing these up can sound unnatural to native Japanese speakers!