I was wondering if there is any reason not to have a system that just uses an SSD for storage.
Other than price and what your budget allows, no.
If you are on a budget and just want a fast boot up, you get an ssd plus hdd.
SSDs have limited write capabilities, so most probably you don't want to use them for something that writes often. Well, if you're OK with throwing them away and buying a new one in time, it's not an issue. :)
This was something that could be a concern back when SSD's first came to market and the technology wasn't mature. That's not the case anymore and it's not something you should worry about unless you're writing 100's of gibs a day to an SSD which is a ridiculous amount. A normal user is looking at 5-25gibs a day. At which point you're looking at wearing out your drive, depending on the capacity, in about 20-100+ years.
LOL for the upvote on your comment and the downvotes on mine. You said the same thing. :D
To be fair you made it sound it something that happens often/easily where as BeerzGod explained how much effort it takes to kill a SSD via writing to it.
I didn't think it sounded anything other what it said: if something writes often, it may wear out the drive. I guess often is a rather loose term. It really depends on an application, and since I did not specify any of this, it is true, that anything could be read out of my comment (even things I did not intend).
There's a saying where I'm from, that says, everyone judges others based on his own view of the word, his own experiences.
That is in this case, that what may be often and a lot of data for one person, might not be the same for another.
Next time, I'll either dedicate more time for a post or none at all. XD