While the question is justifiable, the answer is a bit complicated. If you think about it, SEO does have some immediate results, such as fresh content and a better organized website. If any of the following statements are true for your website, then you need a new one:
- You’re using a non-maintained, open source website engine, like WordPress, Joomla, etc.
- Your website doesn’t comply with Google’s website rules.
(Test it here: https://developers.google.com/speed/pagespeed/insights/) - Your website’s admin system doesn’t support adding at least 8-12 words to the pages’ source code.
So, if you find that any of these statements are true for your website, then you need search engine optimization not only because Google doesn’t like you, but also because your current site is so outdated it costs you a lot of customers (and money).
Of course, most companies pay a lot more if they require SEO, and the main objective is to achieve high ranking in SERPs (search engine result pages).
The consequences of SEO are hard to predict because there are several factors in play when it comes to the “speed” of the results. Such factors include the base traffic of the website, the age of the domain and so on.