You should always be sending "thank you's"; phase I, phase II, scramble, encounters, networking, etc. It is good practice in our community because pharmacy is a small world -- even may seem smaller when your even slightly ambitious. Additionally, it is even more important to be sending them when things don't exactly work out in your favor (ex. not matching, declines for interviews).
I personally have done this and have received back positives response (especially when I have asked for constructive criticism that would help me grow). With that same breath, I have also not received any response despite my email sent in good-faith -- but I know I did my due-diligence and left things on a positive note*.
Personalize them, send in an appropriate amount of time, be personable, and always professional!