Net stock issuance combines two opposite cash flows: money coming in from selling new shares, and money going out to buy back existing shares. The net of the two tells you whether the share count is rising or falling.
A positive number means the share count is growing, which is dilution. Each new share makes every existing shareholder's piece of the business a little smaller. That is bad unless the cash raised is put to work at a return higher than what shareholders expect to earn.
A negative number means the company bought back more than it issued, so the share count is shrinking. That is good when the buybacks happen at fair or low prices, and harmful when they happen at sky-high prices.