Use 'has legs' for ideas or plans that you think will be successful or relevant for a long time. Your renewable energy proposal really has legs; it's the future of our industry.
Pro Tip 2/3
Metaphoric Potential
'Has legs' is a metaphor that suggests something is strong enough to stand on its own and move forward. This application's unique design has legs – it can disrupt the market.
Pro Tip 3/3
Future Success
Use it when expressing confidence in the future success or sustainability of an endeavor. I think this charity has legs; its model is scalable and impactful.