That could happen in a multitude of ways:
1. A site spends a lot of time developing advertisements and obtaining IRB approval and then protocol change is made and then they have to make all new ads.
2. Sponsor wants to capture more details in the eCRF, so they add a new CRF page that has to be completed for all subjects.
3. Sponsor audit is done and auditor mentions that delegation of authority log only says "labs" and doesn't distinguish between drawing labs and interpreting labs, so they make every site study-wide re-do all their delegation of authority logs.
4. Sponsor finds out drug is unstable / DMC results are unfavorable so they immediately shut down study.
5. Protocol amendments
6. Issues with protocol that require study-wide telecons and retraining.
7. EDC guidelines that say one thing but when it's time for data lock, they change their mind and query everything and require sites to change every ug to mcg for every dose amount.
8. There's a new system introduced and you'll need to register for access, complete training and change your processes and procedures.
The list could go on- if there's one thing you can count on in this industry, it's change!