Every business with a competent marketing department will continuously track and measure the effect of the ads they run, like how many users who click the ads turn into paying users.

My startup has tried a variety of marketing strategies from in-person campaigns on the street, video ads on YouTube, "free" PR through newspapers etc. In order to measure the effect of each approach we only did one at a time.

For us paid marketing on Facebook/Instagram was, unexpectedly, the most efficient form of marketing by far. But I would not assume that applies to all, or even most, businesses. So you should experiment with different strategies for your business.