I have brewed many batches where I never checked the gravity in the past. You don't really need to check the gravities to make great beer. You do run the risk of not knowing when a beer is complete and maybe having overcarbonation issues in the bottle. But good fermentation practices should, normally, take care of that.
However, I think that when you get past just wanting to make beer to drink and you really want to start nailing down a great recipe; gravity measurements are part of many different data points to collect. Getting those #s help you to hone in on potential issues. And they also help you monitor consistency batch to batch. A solid process in the brew house yields the ability to build better beer because you are consistent.