[ParvusPonte]

Better memory usage due to the (BSD-like) kernel, vs Linux could be one of the factors.

"My server earlier used to consume over 1 GB of memory for running PHP, MySQL and Nginx. Now, it doesn’t even touch 500 MB! It’s always less than 500 MB. Everything is just same, configuration, etc. Only OS changed." http://nileshgr.com/2013/06/07/the-move-from-linux-to-freebs...

Slightly off topic but I really wish mainstream VPS providers start adopting FreeBSD, perhaps http://labs.online.net/ can spark that change, I'd move from Digital Ocean in a heart beat!

[informatimago]

Well, MacOSX and iOS don't have a BSD kernel (or even a BSD-like kernel) at all. They have a Mach kernel. They have howewver, a BSD-like userland and kernel personality. But I guess we can assume that the Mach kernel is also more frugal than Linux. In any case, AFAICS, Apple takes some care about this, because of the performance and user experience consequences.