“Single web pages” are very popular amongst those looking to present their companies on one-page websites without needing their users to click on unnecessary links that redirect them to different pages.
Showcasing all the content on a single page is especially suitable for non-content-heavy purposes like portfolios as everything is loaded on the initial load or the content below the fold (not yet visible part of the page) is deferred and only loaded when the user scrolls down, which could improve the performance. Not having to jump back and forth between the pages is usually perceived as a more continuous and fluid experience by the user and contributes to an increase in lead generation.
“Landing pages” on the other hand are also displayed on a single page but have different functions. Unlike “Single web page websites” “Landing pages” are purpose-built standalone pages or they could be part of a company's main website and are laser-focused on the so-called “Call to action” (CTA). The content is very limited and the main intent of a landing page is to increase conversion rate — frequently through marketing campaigns by urging visitors to take some kind of action whilst on the page.
There are two main types of landing pages – Lead Generation and Clickthrough.
The Lead Generation pages display a type of contact form as a call to action that aims to collect user data and build a database with good business prospects which can be used later.
The Clickthrough landing pages are more focused on ways to sell a product/service or to sign up for a subscription. An "action" button is often used as a CTA which directly links the visitor to a sales page where a series of upsells and downsells can be performed conditionally while leading the user to checkout. This method is also known as "sales funnel" which usually comes with its statistics and analytics data, used to determine the performance and efficiency of a campaign so that required changes can be made accordingly.