It won't make a difference.
If you want to be sure try to disable the write cache & see if the performance will drop but it will not.
Ziad don't you think it's obvious he could disable write cache to see if makes any short term difference?
He is looking for a technical answer for the long term differences when using the SSD as a cache instead of as a regular drive and not some captain obvious try and see reply's.
Actually, you are way off base, guy.
Write caching and using an SSD as a write cache are two completely different things.
Write caching on the SSD is a performance setting, to reduce the number of writes operations initiated to the drives, it will cache multiple writes, and then perform the operation at a later time. The OP is asking if he should keep this setting on, which will have only a performance hit in a desktop environment.
I would disable this setting, you will likely see.. some kind of small performance hit from the drive, but in the unlikely situation (in a desktop environment) where you have cached writes, and lose power or have a system crash, you don't want your data to be sitting in memeory cache waiting to be written to your system cache (the SSD). That being said, its highly unlikely as I hinted at before, that this situation will happen and its mostly a performance preference.
I have no Idea why you was saying i was way off base when i was saying that a Write caching and using an SSD as a write cache are two completely different things and he should ignore Ziads ridiculous try it and see reply as he needs long term results for the cache to build.
then you go on to say the same.