You'll notice if you make big jumps. If you go from say Altus to acera, you won't notice a thing. But if you go from Altus to acera, you'll notice things work much more nicely. And the parts get a little lighter as you go up the chain. The other thing you get are more sturdy components. Most casual riders won't notice a difference between xt and xtr but the price jump between the two can be quite drastic. If you're handy and can turn a wrench, you could swap out components yourself. It's not that hard and there are many YouTube videos that will show you how. But it's generally cheaper to buy the bike with the stuff you want versus upgrading all of the components.

Then you need to pay attention to the number of speeds that the equipment will handle. Some of the lower end stuff will only do 7 speeds and others 8 and hen as you go up you'll get into 9 and 10 speed. You'll notice a big difference in changing the shifters before he deraileurs. He gear changes are smoother and more direct. You'll notice a difference between acera and xt v brakes as well. The xt brakes will stop you more immediately. And then when you step up to str brakes, those are really grippy.

At the end of the day, if you are just beginning, any bike that you get from an LBS will be vastly better than a department store bike.