There are (IMO) two extremes within the wonderful world of buybacks.  

At one end of the spectrum, are very mature companies, that have little capex, and generate significant free cash flow.  And buy back a somewhat similar dollar amount of their own shares each and every year.

At the other end, are highly cyclical and/or capital intensive companies, that have a habit of buying back stock when they do have free cash flow...typically at the top of their industry's cycle.  Which is exactly at the wrong time.....and at the bottom of the cycle are often starved for equity, and may end up raising equity at depressed prices.

I will say that there were a lot of companies, post the 2008 crash, that had been buyers of their stock at higher prices, that were too frightened to buy back their own stock at depressed prices (probably cuz they had frightened bankers, that might have pulled lines of credit if said company bought back stock).