Simply put, if you try to open a checksum file that has a very large file size, you'll get the following error:

I ran into this because Linux operating systems can have a lot of small files for their OS and stuff (literally millions). And of course, if you use checksum algorithms that result in larger hashes (e.g. SHA256, SHA512), it'll increase the resulting file size as well.
For reference, this occurs regardless of the system RAM - I tested with both 16GB and 32GB and it made no difference.