There are a number of benefits to using shared hosting. The high cost of buying and maintaining a server can be balanced against the income from multiple clients paying to use it, making it the least expensive form of commercial hosting. The is ideal for anyone with no high-level technical skills but who has a web site in need of hosting since your sole responsibility is monitoring your own account. Among the other advantages are the guaranteed up-times, customer support and a contract.
The drawback, of course, as the "host sharing" name implies, other clients are sharing the server with you. There is a finite amount of disk space, memory and CPU space on any server so there is the potential that the service may be slow if there is heavy usage at peak times if the web host has have overbooked the server or if the server itself is simply slow - if this is the case the result will be that your web site seems slow.
Additionally, many dramatic and useful high-end features available to you will not be functional because of shared hosting. There is also the ever present security risk which is slightly elevated when you share a server with other clients but this is negligible since the server itself will be secure to begin with.
Most web sites and users find shared hosting to be an model answer to their hosting needs. There are a minuscule number of people who want or need more control over server contents and the vast majority will never need anything more.