Well I hear about all these High-paying keywords and what If I use those keywords on a site that doesn't relate to the keywords at all? Is that legal? Or are they just suggesting I won't get any clicks being that the keyword doesn't relate to the site at all?
Is it legal? Of course - do you think the keyword police are going to arrest you? Is it pointless? - yes. If you were thinking of putting irrelevant keywords in your keyword tags - well, the major search engines don't pay much attention to them anyway. If you were thinking of using them as adwords keywords, you'll get slapped by google in terms of your quality score and end up being charged something like $20 a pop.
It wont make any sense for you to place irrelevant keywords on your site not based on their topic, instead you could create a site or sites related to those high paying keywords. Your website, its content and displayed advertisements of any type should make sense to visitors, basically dont display mobile phone ads and banners etc on a medical supplies website.