User blog comment:Tricoro/Guide to Ultimate High Score - Endurance/@comment-26044650-20150321140556/@comment-26044650-20150321162011

He ditched Princess Cookie right off the bat because she's only good for the "10% Cool Down of Pets" which will make Enchanted Locket give a mini Energy Potion every 13.5 seconds instead of 15. Otherwise Princess Cookie is VERY lackluster compared to many other Cookies - she doesn't even give you any additional points AND you don't want to hit obstacles anyway. Why even use her at all?

Anyway, it also gives him time to build back up to 100% Energy because he can use the Giant Energy Potions to help. If he just ran with Princess Cookie until she ran out of Energy, Blackberry would still be only at 50% Energy as there's no more Giant Energy Potions to build back up.

I'm pretty sure he did an experiment by using Princess Cookie to the fullest before switching over to Blackberry Cookie and then did another experiment in getting rid of Princess immediately and switched to Blackberry and found out that the latter gave much better results.