The main issue is direct sunlight but teak is very durable compared to most timber species so even direct sunlight will only really effect the colour of the wood in the short to medium term. After decades it will degrade the wood, but most other species would have been destroyed long before teak.
The main advantage is due to its lower moisture content, reclaimed teak is much less likely to crack, twist or warp compared to plantation teak. It is also more sustainable than plantation teak or cutting down old growth teak.
