<p>How many safeties (for which you are assured admission and affordability and which you like) is up to you, as long as you have at least one. If you prefer to have a choice no matter what happens, then having more than one makes sense.</p>
<p>If you are unsure about a school, but are pressed up against the deadline for admission and/or scholarships, you might as well apply, so that you can have the choice in April rather than regretting not having applied.</p>