Just heard from my friend who are experienced SEOer. He told me about minor change which made on title and meta tags will cause site ranking in Google down a few spots initially before ranking swing back. I know this is a process of re-evaluate but I that's only my assumption and don't know exactly why these change cause of this. Anyone can help me clarify this? thank you in advance.
Title tag is a crucial element at 1st SERP. All sites appear in 1st SERP have gained certain authority for the query. So, Google may consider Title tag specifically when choosing the most relevant one. Meta description tag also carries a value for snippet under the title in SERPs. But it cannot be important than title tag and cause noticeable changes.