SSD would use less power and be more resistant to damage than old HDD. They are also much faster than HDD and is useful for syncing and relaying of blocks.
Well, on paper a ssd is way faster than hdd but a BananaPi with SATA 1 Interface and an 10 MBit upload connection won't use nearly the max. read/write performance of the ssd. But an ssd would be useful when supplying many different parts of the blockchain to many different nodes at the same time, right?