This standardization has enabled the rapid development of a very large token ecosystem on Ethereum. Before its creation, each service, each project had to reinvent the wheel (the token), which has caused errors and incompatibilities.
With a simple and open standard, tokens can be deployed easily. This is also the case for services using these tokens. In fact, most of the services developed on Ethereum today manage this standard and only this standard. It is easy to create a service managing the ERC20 tokens because you know in advance the basic functions that this token will accept.
For example, MyEtherWallet and Etherscan are able to display the balance of your ERC20 tokens on its interface, and EtherDelta natively manages decentralized exchanges between all existing ERC20 tokens.