Row hammer exploits. Someone else running on that server can read and flip your ram and generally pwn you.

For personal use perhaps it doesn't.

For professional news having data corruption is not something that you'd like, especially if you handle client data (as in backup) or even more importantly if you handle payments.

Overall for pro use lack of ECC is just a catastrophe waiting to happen.

Wait until you get RAM errors, you probably won't notice it until services quietly start to crash and you cannot figure out why because the errors are not logical. So you try to restore a backup - but then the backup won't unpack because the RAM created a corrupt backup. Having a fancy file system like ZFS won't help, but it might give early warnings (if you scrub often).

I guess you get the picture.