Why does my orthodontist want me to switch trays every week?

Your dentist has the ability to make adjustments to your Invisalign treatment plan based on the specifics of your case.  This means that there is nothing wrong with changing trays weekly, if your orthodontist instructs you to do so.  Good luck with everything.Sarah Thompson, DMD   O'Fallon, Illinois and Saint Louis, MO

The trays may be focusing on a particular aspect
that your orthodontist feels can be accelerated. Irresponsible, accelerated
movement can lead to resorption, but if your orthodontist is seeing you
regularly and knows the specifics of your smile needs, then you should be in
very good hands. 

Your orthodontist can decide ahead of time how much movement
to place into each tray so the time you wear each tray can vary from one week
to three weeks depending on how much movement each tray actually has. You should
follow their recommendation.

Your orthodontist can prescribe the teeth to move in any way they want.  It's the orthodontist who makes the treatment plan, not Invisalign.  I slow down the movements on all of my Invisalign cases, but double the number of trays.  I find this to be more efficient and better for the patient.  Follow instructions your orthodontist gave you.  They attended an additional 2 or 3 years of education after dental school just to study how teeth move.