– You have full control over what your ads say and where they lead. You can use this to send the right message, for special promotions, for putting a spotlight on your most important products…
– Ad extensions can have significant impact on user experience, e.g. sitelinks, call extensions or location extensions
– More space on the SERP
– You actually receive data on your impression share and get access to auction insights
I guess you’ll have to consider whether these points are worth the (probably very low) CPC.