Indicates a stopgap or temporary fix, not a permanent one. A space heater will serve its turn while the central heating is fixed.
Pro Tip 2/3
Current Need
Use when something meets a need or purpose right now, even if it's not the best option. These old textbooks aren't current, but they'll serve their turn for the exam study.
Pro Tip 3/3
Usability
Emphasizes that something remains usable, despite being outdated or not ideal. Grandma's sewing machine looks old, but it still serves its turn.