Think it's normal to give yourself multiple options — if you're broadly happy in your current job but come across a job ad that's more exciting you may just apply for it on its own, as your options are to stay put or accept the new role. Staying put would be your 2nd choice.

But if you're unhappy in your current place, you're more likely to apply to multiple places at the same time — if you find 2-3 jobs ads that are all better prospects, staying put may now be 4th choice. Plus you may want a contingency if you don't get an offer from choice #1/#2.