As a provider of a Saas solution, we are the opposite - we do not want users to need a demo as it increases the cost of sale hugely.
To that end, we do as much as we can to make our trial as user friendly as we can including offering a sample data file so they can try it out using dummy data rather than taking the time to enter their own data (some companies also don't want to enter their data during a trial hence why we have so many trials from companies called Test with 1 employee and in accounting!).
The exception to this is complexity - if the application is complex or the time to value is long then simply letting a user loose to try it for themselves will be detrimental to their chances of closing the customer.
There is a useful article which talks about the relationship between complexity and price in Saas sales models which is really good - basically the more complex a product then the higher the price needs to be to justify the expense of selling and marketing it. In this area then demo's etc are justified and needed but, anywhere else, and then can be an expensive and unnecessary roadblock.