Since I started as an artist, I usually have more concrete ideas of what my main cast looks like. Plus I like drawing them so I'd definitely need a base reference! I don't necessarily show my readers what they look like outside of my novel's cover/banner/thumbnails, and instead keep all my illustrations just on my social accounts. But they can definitely check it out if they want, and I describe my characters as best I can in the text without getting too specific.
I tried Artbreeder but I found it too hard to finagle to get what I specifically want. The starting femme faces are too femme and I didn't want to waste time procreating female children from masc male faces to get a decent result. Don't even get me starting on finding the right facial hair. xD
All in all, I prefer my results from morphthing.com which I then cleaned up on photoshop.
Morphthing essentially combines two photos together to get an average, I used celebrities for mine and then photobashed some of it further.
The unions from left to right: RDJ and Sam Elliott, Gwendoline Christie and Zendaya (with Deadpool burn skin), Anthony Varrechia and Stephen Lang