In case the user is the owner of several websites, then multiple domain hosting is surely going to benefit him/her in reducing hosting costs. The benefit of multiple hosting is that it allows user to host more than one website on a single hosting account. Thus one can have several website at a cost of one.
In general users instead of purchasing a website purchases a hosting account. There are cases where hosting account can only be used to host a single domain and hence a single website while in other cases the account can be used to host multiple domains and hence multiple websites.
As with everything there are pros and cons in case of hosting several domains on a single hosting account.
Talking about advantages the first and fore most advantage is surely cost. It is really cost effective to select an account offering multiple domain hosting as here in this case user gets benefits of many websites at cost of just one. It is quite cheaper way of hosting multiple websites instead of purchasing a hosting account for individual website. Example just consider a hosting provider offering a simple hosting package for mere cost of £70 per annum and U.K. domains for just £2.00 per annum. Thus now for hosting four websites using separate accounts the cost will be £70 *4 + 4*2 i.e. £288 per annum. And now with a single account and multiple domains the cost would be £70 + £2.0 *4 which comes to around £78 per annum. Thus the saving is clearly of £210 per annum.