Yes, they are.
A render takes about 3 minutes on your local system. The server uses a gigantic database (many TB of storage) to cache the rendered results so that you don’t have to wait 3 minutes for each image that you need within the game. The alternative would be publishing the TB-sized library, which would be more expensive (bandwidth in such dimensions gets pricy too) than running a server for doing that. The alternative assumes that you’d be interested in storing thousands of Gigabytes for just a single Visual Novel🙈Also, if you rendered on your local system, you’d have to install hundreds of Gigabytes to be able to do so. Furthermore, it would utilize your system resources by 100% - and on a laptop you’d probably wait for up to 10-15 minutes per image.
Overall, rendering on the user’s device is not feasible. Publishing an image library is not feasible either. Thus, I am left with the option of that server. I will probably allow smaller image packs (that of course restrict, e.g. no clothing options, no customization options) to be downloaded (1-2 GB), if it’s such a no-go for somebody to play with a server, because I do understand that this can be seen critical, as there is no way for you to verify what is happening on the server. But the majority of players will prefer the online mode due to the better graphics.