I asked the lead programmer for Nisus Writer Pro about the performance issues that people mentioned and here’s his response. He’s a great guy, and really does look into problematic files that are submitted via the Feedback mechanism in the app.
The cause of sluggish behavior in Nisus Writer can depend on a variety of factors. I would break down the causes something like this:
1. Files with tons of pages (eg: books with 700+ pages). These are going to be slow due to pagination complexities in Page View. For these kinds of documents it's better to work in Draft View. For some writers that solution is a non-starter because you can't see or edit footnotes/endnotes in Draft View. The good news is that we're working on a future version with new features to help with that.
2. Files using a lot of complicated features like tracked changes, cross-references, etc. These we'll have to tackle on a case by case basis as we see the files, since often the cause of the slowdown is degenerative behavior in the code that wasn't anticipated.
3. Files with large images that take a lot of space. I'd actually be surprised if this is really the cause of slowdown for any users, at least with regard to opening and editing files. It's quite fast to read data off the drive, new APFS or not. What might be more troublesome is the save time. As autosave engages frequently, even a few seconds to save a large file can feel like an eternity. One possible solution is to use our custom Nisus Compressed Rich Text Format (.zrtf), which has much greater efficiency when saving (over regular RTF).
Well, if any of you have documents to share with me, that exhibit abnormal slowdown when they're opened or saved, please let me know and I'll see if there's anything we can do.