Live Chat combines the advantages of instant help from support hotlines with those of e-mails allowing you to copy and paste information.
It's also great if you simply prefer to communicate in written form, whether for convenience, personal preference or documentation purposes.
Live Chat doesn't necessarily mean that it's 24/7 support, but often the hours tend go beyond usual office hours. There can still be queues, but at least you're not stuck listening to on-hold-concerts or advertising.
The list below shows you which domain registrars offer live chat. Domain Raccoon also provides a list of registrars who offer phone support or 24/7 support.