inodes
I am temporarily with ChemiCloud. I say temporarily, because although they promise me 20GB of disk space on my plan, I only get 250,000 inodes, and I am currently using 181,690 of them. As per their general resource usage policies, if I exceed 250,000 inodes, they can suspend or even terminate my account.
I'm currently using 73% of my allocated inodes, but only 16% of my disk space. Which means that I am paying for disk space that I can never use. As I use an AWS S3 instance to hold backups and audio and video files, I will never have enough large files on this host to use up that space without running out of inodes.
I have found that a lot of web hosts have these limits, such as VeeroTech, Geek Storage, SiteGround, StableHost, and Hawk Host (which have the largest limit—500,000 inodes on all plans—that I have seen).
If I were simply coding things by hand, this would not be as much of an issue, but as I tend to use CMSs a lot (WordPress, MediaWiki, DokuWiki), this is untenable, because these packages have a lot of files.
Some of these companies tell you straight up what your inode limit is, but for some of them, you don't find out until after you sign up, unless you make a point of asking beforehand. For example, the only thing I could find on SiteGround's site was this knowledgebase article that mentions why limiting inodes is necessary, but it still doesn't tell you what that limit is. As another example, I cannot find anything on Hostwinds' site about inodes limitations, other than this article in their knowledgebase that talks about inodes and their limitations, but doesn't provide a specific number.