Benefits of SKU as Product ID

1st Benefit
At every stage of advertisement, analysis, correction, and optimization, everything is shown with the reference to the ID of the product.
If the product is the SKU, it becomes very easy to recognise the product rather than having long ambiguous string and numeric characters.
For example:- While creating Product Groups in Google Adwords and analysing the reports, you can easily monitor and recognise your products and performance and group them accordingly. 

2nd benefit
If you are using Shopify’s Global ID and suppose, you accidentally deleted a product or if you are a Dropshipper and you are using any 3rd party app like Oberlo or any other similar app to add products to your store and now suppose if one of your best selling product inventory is out of stock by a vendor.

Now when you add the same product of another vendor using such app, then Shopify will consider it as a new product, the Product IDs will change in Shopify and in Google Merchant Center. 

Every product with a new ID is a new product for Google, its performance and everything starts from Zero and you will lose all the performance History of the product, that has been replaced.

Now, if you are using SKU as Product ID and you add a new product which is exactly same or appreciably similar product, then you can use the same SKU for the newly added product and when you add a new similar product, the ID in the Shopify database will change, but the ID for Google Merchant Center and the entire Google Ads Environment remains the same You won’t lose any performance history as you are submitting the same product with the same ID and unchanged SKU.

3rd benefit
If you are not a drop shipper, but sell the products manufactured by you, and later decide to change the Selling platform(for example Shopify to any other platform or from any other platform to Shopify)Your marketing efforts won’t be platform dependent. 

If you are migrating to any other platform or from any other platform to Shopify and SKU as ID feature is available on the previous and current platform then your Performance History, Marketing Activities & Analysis won’t change and will still continue to be used for future campaign activity performed by Google.

In short, all your Clicks, Impression, Product Reviews, Performance history attached to the ID will not be lost during the migration of platform.

4th Benefit
If you are using SKU as Product ID, it becomes very easy for Google to map Product Ratings from Product Ratings Feed to Product Data Feed
Also, it is recommended by Google itself to use SKU as ID. 

Here are some Pre Requisites of using SKU as ID
Each and every Variant must have a unique SKU assigned.
Google and our App allows a Character limit of 50 characters for SKU. 

However, we recommend you to have around 20 - 25 characters of SKU because Google has a limit of 50 characters, but you when you migrate to other platforms, it is not (Shorten the gap) Guaranteed that they support 50 characters. 

So, if they don’t support longer SKU characters, then you will have to change SKU ID which may lead to loss of performance history.