I haven't used specifically Google Surveys to create content but have heard from others who have used it that it’s a great method to obtain data that can be turned into content or infographics with unique stats. This is a great SEO strategy to use for acquiring new backlinks which will help contribute to a site's authority over time. You can use the data from the survey to create an informative piece of content and/or infographic with unique and interesting stats. This will give you a linkable asset (high-quality pieces of content that attract backlinks or social shares) that could provide valuable/quotable stats that journalists or those within the given industry can cite or discuss in their own write-up on the topic or simply add a link on their site back to the content from a relevant resource page.
You could also get an email list of your client’s customers, and send out a general survey to them using something like Google Forms or Survey Monkey’s basic option (free for up to 40 responses I believe). For example, an HVAC company can send out a questionnaire to their customers asking about the last time they’ve had their appliances serviced (water heaters, a/c units, etc), then also ask things like when was the last time something like that broke in your home? Or how many times a year do you need a plumber? Then you can take all that data and make some cool infographics and content for your site. And then you can use this linkable asset to reach out to relevant home-related publications or blogs and say something like “did you know, 50% of homeowners in [city] have no idea when their water heater was installed or the last time it was serviced. And within the content, you could provide tips to homeowners including maintenance schedules or what to look out for. The idea is to share these interesting stats and information to those whose customers/readers would find the content valuable and see if they can use the info on their site or include it in the next relevant blog or article they will be writing and hopefully get a link back to the content
And as an agency, if you had 100 law firms across the US/Canada, for example, you could survey them to get data behind average case type, settlements, case length, monthly leads, etc and break that down into some really cool content for your agency’s site and get “industry” related links.
If you have the time and resources to create new surveys or even use existing data to come up with a unique analysis of said data (crime reports, injury stats, etc) and then create new and unique content with the data, it’s a great SEO strategy to use, helping to increase the number of backlinks to the client's site (SEO benefit) and potentially positioning the client as a thought leader in the given industry by providing relevant and useful information to the community (brand awareness).