What is the main benefit for the investors when a company announces a stock spit?

A stock split reduces the price per share, making the shares more affordable to smaller or retail investors. This does not increase the market capitalization or shareholder value but makes trading easier by improving liquidity and accessibility.

References:

Volume 1, Chapter 8:Equity Securities, section on "Stock Splits and Consolidations," describes the purpose and benefits of stock splits for investors, particularly in terms of affordability and liquidity​.