Carefully planning your photoshoot allows you to better manage your time. Planning your shoot means you know when, where, how and who you're doing the shoot with. But, honestly, there is something about not planning the shoot.
Pros from an unplanned shoot are the random locations, raw emotions and the fun you have while doing it. These unplanned shoots end up in road trips, which happen to be really fun. It gives me energy and motivation to wake up and decide to do a shoot. Not planning your shoots also has cons, which can vary from bad time management to not reaching the goal you had in mind.
I could say that I'm very fortunate that I have always reached my goal. Time management will always be a problem if you do not plan a photoshoot. Good thing I always do these things on my day off.