I have an issue very similar to this previous question.
When I use my signature snippet in an email in Salesforce Lightning, it adds extra spacing that I don't want. The signature has a couple of links - when I remove those links it does not add the extra spacing.
It does not add the extra spacing elsewhere.
Here's an image of it with the links enabled, in an email:
And an image of it without the links, in an email:
Hi, and welcome to the forum! 
Unfortunately, this double spacing issue does occur on a few sites that use certain types of text editors. It actually works correctly in most of Salesforce as Salesforce uses a wide variety of technologies.
Could you provide instructions how to get to that specific editor in the SFDC UI? Using the "New Email" link I get the editor below where the issue doesn't show up (you can see by looking at the icons that this is actually a different editor technology than the one in your screenshot):
In the meantime, plain text snippets will not have this issue like you observed.
A solution to the same problem I was having, ended up being in the SF settings for my profile. If your permissions allow, you can go to
Profile 
Settings Email My Email Settings
From there, you can pop your signature in the box. Or, if you want to get all fancy, you can put the HTML code of your signature in the box. Then select whatever check boxes you want/need on that page. Now any email you send or reply to will have that exact signature in it.
Personally, I recommend the HTML code since you can control line spacing. If you would like further insight on how to get the HTML code for your signature, specifically for Salesforce Lightnings use, I’d be happy to help. Took me trying a few methods before getting it juuuuuust right.
Cheers!
Thanks, Scott.
I usually use the expanded email editor, so I'd click the two diagonal arrows in the upper right corner of your screenshot.
I'm not sure if it makes a difference, but my screenshot was also in reply to an email rather than creating a new email. I tested from creating a new email and saw the same spacing.
My only other thought is that SF admins seemingly can customize the snot out of everything so I'm wondering if perhaps my view just has more options.
Thank you ! My only problem with this is I have several versions of my signatures, in different languages. So including my English signature when sending to a Portuguese customer wouldn't be ideal.
I appreciate your help !
