A treatment is comprised of a feed-wide design or group of product set designs.
Single Treatment Feed
Pros: manage one treatment for all ads; can still create call-out designs for product sets within the treatment
Cons: Affects images on all ads using the catalog; cannot select which campaigns/ads receive the treatment
A Single Treatment Feed will replace the main image link of your feed with the new treatment. Linking a single treatment feed to your catalog in Commerce Manager will push the treatment to all ads accessing that catalog.
Single Treatment feeds are the easiest option to manage as any published updates to the treatment will automatically be updated across all campaigns without having to manually adjust anything on the ad level.
Multi Treatment Feed
Pros: Explicitly assign creative to individual ads without affecting every catalog ad in your account; higher control over where Enriched Catalogs are run; Can still run standard DPA with or without its own treatment
Cons: Assigning treatments to live ads counts as a change to the ad creative; cannot use slideshow option within Facebook settings
A Multi Treatment Feed will retain the main image of your feed and add the treatments as additional images within your catalog. Creating a Multi Treatment feed allows you to assign specific treatments on the ad level to any campaign you'd like, without affecting the other campaigns.
Multi Treatment feeds provide you with more control over your viewers ad experience. Once a treatment is assigned to an ad, you can switch a design out in the treatment, without editing the ad again.
You are also provided the option to set a primary treatment, which will be used across all catalog ads without an explicit assignment.
Because both Slideshow in Facebook and the Multi Treatment feed use your feed's additional images, if Slideshow is turned on for an ad, it will end up showing all of the added treatments for the feed which can lead to undesirable results