This is purely a method to save money. My wife and I did this at our wedding.
Since the venue or caterer may not let you bring your own appetizers (which can often be gotten very cheaply compared to what the caterer will charge you), we put cookies on our tables. The caterers will not stop you from providing desserts. And here is the trick, not all the desserts have to be sweet. You can put out savoury desserts instead. Put a large plate on each tables with mostly cookies, and then hide some pretzels and nuts in there too.
Yes, this is sneaky, but you know you’re spending a premium for many wedding services. If you’re very budget conscious, and this helps you out even a little, I’m happy for you!