As a reader, think about the appeal of a page that has some space between the lines and in the margins. If a page is too crowded with text from top to bottom, it is not only difficult to read but it loses the reader’s focus.
The same is true of the slides in your presentation. The equivalent principle applies.
Leave enough white space to make it easy for the audience to focus on critical points. Remember that you want audience attention on you, the presenter. The slides should be incidental to your talk and enhance, not overtake your message. If you crowd slides with multiple points and graphics, you confuse your audience and risk losing their attention.
It may be hard to let that great picture go or delete those moving arrows but, if they crowd the slide and divert attention, do it.
No crowding allowed!