The space will fluctuate as needed. The cache will fill up as you visit more sites, this makes it faster when you return to sites. Then the cache will empty old stuff as new stuff is cached.
Apps are kind of like a browser too, especially streaming video and picture apps. They have caches of data as well. Especially free to play games that download ads to show you. These caches will fluctuate as well. Some have small caches where only pictures of ads are shown, others have large caches where they show videos or have mini-games for you to see.
Messaging apps are the ones that usually have the largest caches, this is so they can save every picture and video sent and received with your contacts. Not that you really need to be concerned with either, but it is a place where space is regularly consumed. These generally don't decrease, they tend to grow unless you delete conversations with lots of pictures/videos in them occasionally.
Until you run out of space, there is no need to be concerned with it.