How many times have you heard that statement? Probably way too many to count! Jesus, I can hardly imagine the amount of times I have heard this. However, it is an important question to ask before rolling. I like to think of this as the "controversy" in pot culture. This is the big divide. There are those that like spliffs and those that do not like spliffs.
I will make the assumption that most people that like spliffs also like having a straight-up joint. I don't think I have ever heard somebody complain that "just weed tastes nasty, and they need tobacco in it." Sure, some may argue that spliffs are less strong for obvious reasons, but if someone is worried that a jay is too potent or too weak, they can simply change the amount they are smoking.
On the other side, people that like joints can be resentful of spliffs. Spliffs have tobacco in them, and this can be pretty scary to the non-cigarette smoker. Cigarette smokers spend tons of money a year on an activity that is not even close to comparable with marijuana smoking. Plus, some people just don't like the taste. Enjoying the taste of tobacco is usually an acquired taste and can normally turn a lot of stoners off. Perhaps, like black coffee, spliffs are something you learn to enjoy.
However, as many smokers will tell you, the effects of spliffs and joints are pretty different. While, quite obviously they taste completely different, their effects are perceivably different as well. Spliffs give an easier and calmer high that allows the smoker to function more easily. Spliffs are nice for doing your chores, reading a book, and relaxing after work. Jays give you a much stronger high that isn't eased in and out. It is good for your weekend hangouts, gatherings, and video game splurging, but in my opinion, put you are out of commission for a couple hours.
The choice is yours, but I would always weigh in for a spliff. No matter what, I enjoy it a lot more. Plus, it is good for the bank. Instead of rolling all your green gold away, save it and mix it with tobacco. Your wallet and productivity will thank you forever.