One of the most practical benefits of working in related terms is that it naturally reduces the temptation, and the need, to repeat your main keyword too often.
Repetition Reads as Unnatural to Both Readers and Algorithms
Content that repeats one phrase excessively tends to read awkwardly to a human and can look manipulative to a search engine evaluating quality.
Related Terms Let You Say the Same Thing Different Ways
Swapping in a genuinely relevant related term instead of repeating the exact phrase keeps the writing natural while still reinforcing the topic.
Check Your Draft for Over-Reliance on One Phrase
A quick review of how often your primary keyword appears, relative to related terms, often reveals an easy opportunity to diversify the language.
Next step: Use the LSI Tool to find natural alternatives to your main keyword before you finalize a draft.