When enabling Indeed Apply, you allow the candidates that find your job on Indeed.com, to apply directly on the website - ignoring your application form.
Candidates that apply using Indeed Apply will be visible in your Traffit with only basic information:
phone number (optionally)
consent from Indeed.
By enabling Indeed Apply, you agree on Traffit sending the information about the status of the candidate (if he applied for this process using Indeed Apply) and it's changes to Indeed, on the basis of Indeed's Privacy and Terms of service. This data is being sent to Indeed for statistics purposes.
Your adverts sent to Indeed will have an "Easily apply" or synonymous button instead of "Apply on the website" with a redirection to your Career site.
If you want to turn off Indeed Apply, here you can find a tutorial, how to do that.