Sci area is generally the top periodical in all fields, area 2 is the advanced periodical, area 3 is the second, and area 4 is more common. Sci area has the highest influence, equivalent to the international champion in sports, and its representative scientific research level has reached the highest level in this major. You can imagine the difficulty of sending an article in SCI area.
Sci is one of the important indicators to evaluate the academic level of a country, a scientific research institution, an institution of higher learning, a journal and even a researcher.