Understanding an influencer’s specific niche is crucial in planning an influencer marketing campaign for several reasons:

1. Relevance: Relevance is vital in influencer marketing. Influencers specialize in different subjects and their audience follows them for specific content. If your product aligns with the influencer’s niche, their audience is likely to be more interested in your offering.

2. Engagement: An influencer well-versed in their niche can create engaging, authentic content that resonates with their audience. This can ultimately drive better engagement rates for your campaign.

3. Trust: Followers trust an influencer’s recommendations within their area of expertise. Teaming up with an influencer who is a good fit for your brand can therefore foster trust and help increase conversions.

4. Performance Metrics: Focusing on the influencer’s specific niche can improve your campaign’s target performance metrics, be it engagement, reach, or conversions, by ensuring relevance and authentic audience connection.

Platforms like Flinque, for example, assist agencies and brands in influencer discovery, taking into account their niche, engagement rates, and audience demographics amongst other factors. Other platforms like AspireIQ, Traackr, also provide solutions for this aspect, though their features and approach may differ, and thus suitability depends on team needs.

Overall, enlightening yourself about an influencer’s niche, using the noted benefits and utilizing platforms that cater to this need, ensures an optimized, effective influencer marketing campaign.