Using Laravel Join

• Large data sets requiring high performance.
• Queries that need only a few specific columns from multiple tables.
• Scenarios where you need optimized SQL queries with fewer database calls.
• Use join for complex queries involving aggregations or specific optimizations.

Using Laravel Relations

• Smaller data sets or when lazy/eager loading can be leveraged effectively.
• Maintaining clean, readable, and reusable code. Projects
• with a heavy focus on object-oriented design.

In Simple words....

For large data sets, go with joins to optimize performance.
For medium to small data sets or when focusing on maintainable and readable code, use Eloquent relationships with eager loading.

Note : If you're dealing with extremely large data sets, consider using chunking or pagination with either approach to avoid memory exhaustion.