I normally hook it up to a 2nd display (TV) that I use to send pictures of handouts, NPCs, etc. In a few cases, I used it to display the map with the grid set to 1" and put the minis on there, or used digital minis.
The main thing I use it for is campaign prep and to run the combats, track party loot & inventory, XP tracking, etc. I create a campaign book with whatever I think of for my campaign and then before the session, I save important elements to the hotkey bar so I can pull them up quickly whenever I need them. I keep other stuff there such as list of names, professions, generators, etc. There is a mad-lib style system called Story Templates that lets you build story text with table driven content. I used to use this for quickly creating tavern names, NPC names, etc. Now-a-days, I mostly use chatGPT on the side for this. Running the combat in the combat tracker is super nice though.
The party loot and inventory tracking is nice. For IRL games without FG, someone always ends up being the note-taker/party mule. If they don't make it to a game you have to hope that they left the list behind. I still let players write down their belongings, but because I am handing it out as the GM, I keep it in FG as well and then I can quickly verify who owns what. Yes, you guys had 12 axes, 4 shorbows, 6 leather armors, and blah blah blah that you got from the goblin camp. You can sell that back in town. Make a diplomacy roll to see how well you barter... okay, you rolled well so I set the buy back rate at 60% instead of 50% and click a button. Okay, you all get X gold, Y silver, and Z Copper each.
Who is holding that contract signed by the arch-devil? Let me look... okay, it is blah.
Hidden rolls of enemies against passive perception. NPC on NPC violence. Looking up stats and abilities, spells, items, etc. I find it faster than flipping through multiple books.