The thing about SEO in 2018 is that Google changes its algorithms more than once a day! Reports say that the company changes its algorithms up to 600 times a year. While the majority of those updates consist of smaller changes, among them is the occasional, major update like Hummingbird or Panda that can really wreak havoc with your traffic and search rankings.
In 2007, Google announced a campaign against paid links that transfer PageRank.[29] On June 15, 2009, Google disclosed that they had taken measures to mitigate the effects of PageRank sculpting by use of the nofollow attribute on links. Matt Cutts, a well-known software engineer at Google, announced that Google Bot would no longer treat nofollowed links in the same way, to prevent SEO service providers from using nofollow for PageRank sculpting.[30] As a result of this change the usage of nofollow led to evaporation of PageRank. In order to avoid the above, SEO engineers developed alternative techniques that replace nofollowed tags with obfuscated Javascript and thus permit PageRank sculpting. Additionally several solutions have been suggested that include the usage of iframes, Flash and Javascript.[31]
It increases relevancy: Siloing ensures all topically related content is connected, and this in turn drives up relevancy. For example, linking to each of the individual yoga class pages (e.g. Pilates, Yoga RX, etc) from the “Yoga classes” page helps confirm—to both visitors and Google—these pages are in fact different types of yoga classes. Google can then feel more confident ranking these pages for related terms, as it is clearer the pages are relevant to the search query.
The Featured Snippet section appearing inside the first page of Google is an incredibly important section to have your content placed within. I did a study of over 5,000 keywords where ranked on page 1 and there was a Featured Snippet being displayed. What I found was that when was ranking in the Featured Snippet, the average click-through rate to the website increased by over 114%.
Conversely, if your business is in a tight spot, you can decrease your budget or stop spending altogether. You can also specify when you advertise, so if you are having a sale this month and want to reach a larger audience, you can run a campaign focused on the sale just during this month. Or, if you offer special deals on Tuesdays, you can schedule your ads to run only on Tuesdays.

Well, yes and no. Sure, you can get hit with an algorithm change or penalty that destroys all your traffic. However, if you have good people who know what they are doing, this is not likely to happen, and if it does, it is easy (in most cases) to get your visits back. Panda and Penguin are another story, but if you get hit by those it is typically not accidental.