So the original question - "What do you use your laptop for at an event besides playing music?"
At an event? I only use to play music.
Not at an event? I use it to download new music, work in my event planner, and anything else related to my DJ business.
I bought my laptop as a tool for my business, so that's all it is used for.
Now, you ask, what can you use it for? You can use it for anything. You use yours for Monopoly? Great for you. If that works for you, great. I've been working with computers on a large scale (the company I currently work for has over 20k pc's). I start there as a Help Desk associate and have worked my way up through the past 25 years into an IT Leadership role, so I say I have a little experience with computers.
You can add and play games and apps, and maybe they don't affect your dj or lighting software. However, there are usually processes running in the background that are consuming resources that could be used by your dj software. Some folks know and understand this and know how to resolve, but a lot don't. The more you use your laptop or pc (or tablet) for things other than DJ'ing, the more chance you have of introducing lower performance and/or issues. The last thing I'd want is to be playing "here comes the bride" at a ceremony and my laptop reboot because Candy Crush had a random security update and forced a reboot.
Yes, that's a little far-fetched, but that's how it works. Trust me, the updates and reboots always come when you think they won't. If you use maintenance windows, even better... but if you're doing that, you know this entire thread makes you chuckle and pull your hair out anyways. ;-)
I know Dj's running $3k laptops, and I know some running $300 laptops. They both get the job done. I will always say that the more things you add to a device, the greater risk you run. That's not to scare anyone, just to be aware. I'd say this day in age, if you're starting out, as cheap as some things are, I'd recommend you just buy a $300 Walmart pc for DJ'ing and a $50 tablet for your games and be done with it.