Power Query Tabel.Buffer Correct Use
No, that won't work.
Your second query will issue another query of its own.
Buffer can help if you are reusing data within the same query, like referencing the same set multiple times.
Keep in mind in Power query there is a memory limit for the amount of data that will be put into memory, around 256MB, after that will start paging the data.
Consider having a look at this link from Chris Webb for an example:
improving-power-query-calculation-performance-with-list-buffer