You probably should have asked, "Assuming I'm not trying to take pictures for my job, what are your opinions on purchasing expired film?" I will assume this below.
I think most people would say for black and white film stocks think nothing of it, and give it a shot. Some even like to use expired film, either to save money, or just for the surprise aspect of seeing what they will get. Unless a B&W film is many years beyond its stamped expiration date, all you will probably notice is a little increase in the base density. This increase in density adds equally to all gray shades and thus simply adds a small time to what is required during printing. The exception would be if you want to reversely process the film to make B&W slides. In this case, you will probably want to use fairly fresh film to keep the film base as transparent as possible. The other possible downside, in my mind, is that very old film stocks tends to have more of a semi permanent curl to them as it has been spooled up for so long.
For color film stocks, the fear is that the different colors will fade at different rates and cause undesirable color shifts. Color shifts can be corrected during printing, but it is more difficult than just a single increase in time. I say it is a fear, because many get results acceptable to them with outdated color film; however, as the saying goes, "your mileage may vary."
For the record, I have had excellent results with outdated Fuji color slide films (e.g. Velvia and Provia) - to the tune of 4-7 years beyond the expiration date. This is film I had purchased and stored in a refrigerator, so I know its history. I was pushed to give it a try because these film stocks have lately become so expensive, at least for me.
Denis K