As most other blockchain assets without own blockchain, ERC-20 tokens are mainly a crowdfunding mechanism for businesses (in theory, even charities can use them). Their product may vary like
TastyChillySauce00 wrote here, so the grade of innovation is tightly related to the product, not the token itself.
In general one can differentiate between utility tokens (which have again subclasses like governance tokens), security tokens and some special types.
Utility tokens are used to be exchanged to functions on a platform or services of a company (for example, credits in apps). This name is often also used for tokens which can be exchanged for a future service and for those which are used to pay variable fees. Some jurisdictions like the EU require an utility token to be exchanged to an existing service,
Governance tokens is a special kind of utility token which provides a right to vote in a DAO.
Security tokens are tokens with the character of a security, i.e. their value depends on an effort of the company (like a stock). Most RWA tokens (real world asset) tokens, pegged to a "real world" asset like a stock or real estate, fall also into this category.
Special types include stablecoins and some exotic DeFi tokens which can have complex rules.
A nice guide of different token types, use cases and regulations can be found
here. Almost all of them can be created with the ERC-20 standard.
I second however the opinion that most ERC-20 tokens indeed are used for purposes which aren't really worth an investment (only for short-term speculation). In most cases, IMO there is no need to use a blockchain for the supposed application.
PS: Forgot one use case: some ERC-20 tokens are used to bootstrap an altcoin with an own blockchain. The ERC-20 token then will be used to conduct the ICO, while the developers work on the real blockchain project, and later the ERC-20 tokens are swapped to coins on the final mainnet blockchain.