That is right. Doing giveaways is the best method for keeping traffic in your website. But you should do it carefully such that you don't end up loosing too much in the process.It is good to giveaway on the website to get traffic on your site, but it shouldn't be all the time because If you decided not gives again, people will leave the site
As often as you want your customers to stick to you.I do givewlawsys and some discount once in a while to my esteem customers, who always enable me make more sales. That's just a token to encourage their continuous patronage.