why is the sign-off of your email important?

When you are finishing an email to someone, who is maybe your client, your supervisor, your customer, your friend, etc., one question is that how to end up the mail with an appropriate format. 

The sign-off is much more important than you think, because it is the last words that the recipient reads, which deserve you to spend some time to consider how to end up your email.  Doing it right just like that you finish a presentation with an impressive ending.

Here the followings are some references from Justin (https://www.inc.com/justin-bariso/why-your-email-sign-off-is-more-important-than-you-think.html)

Regards: One of the simplest, most common ways to sign off, but percentage-wise, I don't use it that often. Mainly if I'm communicating quick information, or if I've already done something nice in the email and I don't want to overdo it. For example, I sent the following message to someone I met recently on LinkedIn:

Hi, ____,

Really enjoyed your article on recruiting (found on Twitter). Will share later today.

Regards,
Justin

Best regards: I use this one a lot more, often when relationships are new. I view it as a step up from "Regards."

Kind regards: I use this one, too, because I think everyone should be kind. I seem to use it often with women, albeit subconsciously. (I believe this stems from my parents' attempts to teach me chivalry.) I also use "Warm regards" occasionally, but with persons I know better.

Best: This is for variety--an alternative to "Best regards." Now that it's ubiquitous, I use it much less.

Sincerely: I use "Sincerely" when I'm reaching out to someone who may feel I'm trying to take advantage, or who will hold the (perceptibly) less advantageous position in our relationship. I also use it if I'm giving a compliment and I'm afraid the person might question my motives.

 

Hope the above will be helpful for you.