The footnote separator line and the empty paragraph are styled as ‘Normal’, so if you’ve adjusted the paragraph spacing (leading) above and/or below in the style, you may get way more space than you need, as shown in the screenshot below.

When you insert a footnote in Word ( References tab > Insert Footnote), by default it gets added to the bottom of the page along with a short line and an empty paragraph to separate it from the body of the text.