For instance, wear leveling means that parts of your data might be stored on
the drive and you have no way of wiping it, when the controller in the SSD
remaps flash cells.
Encrypting that is useful for security purposes. Encryption always (emphasis
on the word always) improves your security and privacy (obviously, depending
on the key strength, what algorithms you use, what software you use - e.g.
luks/dm-crypt).
I use encryption and RAID1 on 2 SSDs (different brands, to avoid having
similar MTBF) on my own T400 that I use. I don't notice any real CPU overhead
or performance issues with it.
RAID0 or RAID1 on 2 1TB HDDs will also give you a noticeable performance
increase, over just 1 HDD. It won't be as fast as an SSD, of course. If you
use RAID1, an optimized setup will at least mean that read speeds will be
higher, while you get extra guarantee against data loss. I generally
recommend RAID1 instead of RAID0 - the performance gain with RAID0 compared
to RAID1 isn't actually that much, in the real world, because of how RAID
drivers work.
