Enhance is a great tool for integrating services and their SDKs into your app quickly and simply, but this simplicity can come with a surprise or two if you don't realize exactly what Enhance is doing.
When you Enhance your app, you are including SDKs that you pick (such as AdMob or Facebook) in your app. These SDKs are added to your app just as if you had integrated them yourself - except with Enhance you are clicking some buttons and letting Enhance do the hard work. Once Enhance has done its job, those SDKs will be included in your app, so in the vast majority of cases you'll see a filesize increase after Enhancing.
The question we often get is "why is it increasing my app size by 5-10mb?". The simple answer is, that's how big the SDKs you've chosen to integrate are! This is especially true with large mediation SDKs like Appodeal and AdMob Mediation, which include many frameworks and support classes as well as resources from many ad networks, and these can easily add up to the size increase you are seeing. Enhance's overhead is negligible, and you'd find that if you integrate the same SDK configuration manually, the end result would be almost exactly the same.
If you are concerned about your app's filesize then the best option is to choose less, or at least different, services to integrate when you Enhance. In particular, single ad services tend to be smaller than mediation ad networks (they do not have as many dependencies), and services such as analytics tend to be more lightweight than ad services. Also, remember to remove all SDKs from your own source code, if you are using Enhance for those services.