The track spacing is different between 1.44s an 800s. It's like formatting a DVD as a CD-R. (Not that you can actually do that, but the analogy stands.) Data integrity falls through the floor when you do this. It'll work in a pinch for a simple file transfer, but not as a means for any kind of long-term storage. The disk will fail.
Definitely in the case if the 1.44M floppy was formatted as such before hand. So if the box says "Formatted for IBM-PC" or "Formatted for Macintosh", they're be problematic. When you format it as 800K, the track spacing changes, but those old 1.44 tracks are still interleaved in between. They're reel havoc on your data integrity. You'll have serious read/write errors. The only way you can improve that is to use 1.44s that have never been formatted before. But even still, it comes back to the whole "it'll work in a pinch, but not for the long term". A floppy is not just a floppy.
Definitely in the case if the 1.44M floppy was formatted as such before hand. So if the box says "Formatted for IBM-PC" or "Formatted for Macintosh", they're be problematic. When you format it as 800K, the track spacing changes, but those old 1.44 tracks are still interleaved in between. They're reel havoc on your data integrity. You'll have serious read/write errors. The only way you can improve that is to use 1.44s that have never been formatted before. But even still, it comes back to the whole "it'll work in a pinch, but not for the long term". A floppy is not just a floppy.