The legal standpoint differs depends on where your website is hosted and where you are offering your service, and also on what service you are offering. And to that end, it is better that you seek proper legal advice from a local source.
Do you have some specific concerns regarding your site(s)?
In most jurisdictions, there will be a whole host of common law or legislation that will take precedence over anything you put in your T&Cs.
Rarely will T&Cs offer you full protection, but they can help complement your local laws.
In the UK, for example, there are some default provisions under the Distance Selling Regulations (2000) which offer customers greater protection than you are obliged to offer. E.g. if you sell a product to a consumer, the buyer has 7 days to change their minds and ask to return their purchase. By default, the seller is obliged to pay for the 'restoration' of these good, but the T&Cs can specifically over-ride this default clause, and place the onus (i.e. expense) of returning the goods (back to the seller) onto the buyer.
EDIT: In the UK, there is a requirement under the Companies Act 2006 for a commercial website to clearly list the address and company registration number for a site selling products or services in the UK, or whose owner operates in the UK. Not specifically a T&C issue, but a demonstration that certain jurisdictions do impose requirements on you.