Yeah, there is a lot to it. Firstly, if you have loads of ram, and don't really use it, then discussing swap is pointless, just don't have a swap device. If ram on your system is marginal for your workload, then swap is a must have as your system will gain performance by being able to swap, even if it is to an SSD. In that case your system will start swapping to ssd as it gets closer to being full. Zswap improves this by using the margin the system has in ram at which it would swap, to compress the pages in ram instead. So you don't lose any usable ram with zswap. But you gain performance as compressing the pages in ram is faster than writing them to SSD. But it does eat some CPU load in doing this.