The card breaks even only if you use the bus — check your itinerary first
Run the numbers before you buy. Alhambra General ticket: ~€19. Cathedral: ~€5. Royal Chapel: ~€5. That's €29 of monuments. Add four bus rides (two return trips to the Alhambra) at €2 each and you're at €37 — exactly the Basic card price. The Parque de las Ciencias (€9 on its own) and Monasterio de San Jerónimo are then free extras. If you're not using the bus at all (walking up to the Alhambra, say) and only visiting two or three sites, buying tickets individually is cheaper.