When you are composing an email template of signature there are two options for line spacing. By default, clicking return/enter will put a space between the lines like this:
If you don't like how that looks, you can add a single space by using the SHIFT + ENTER. This will consolidate your lines of text so they're not so spread out.
New paragraph with 2 lines of spacing = ENTER (Return)
New line with 1 line of space = SHIFT + ENTER (Return)