I had issue to upload picture in news feed web part in SP 2016 site. I found below article to resolve issue with the help of powershell script. Once i ran the script, its works fine and found that respective app pool added in web application user policy.
Adding or updating Web application policy with new users or groups will trigger a SharePoint Search crawl over all content covered by that policy. This can reduce search crawl freshness and increase crawl load. Consider using security groups at the policy level and add/remove users from security groups to avoid this.
Regarding above statement if we add or update users in user policy, it will trigger search crawl all over search content source. In my case the app pool did in web application user policy, what would be impact in terms of Search level? will it trigger full crawl?