I've gone back and forth with using a laptop for GMing during play. Ultimately, while I've always found word processors useful for planning sessions because you can add onto individual notes without having everything scribbled everywhere in a haphazard fashion, connected with a complex system of arrows, etc. (as inevitably happens when making paper notes), I generally prefer keeping notes in a notebook. Or used to, anyways. Mostly because a large volume of notes (for a campaign, for example) is more easily searchable in a well-organized binder. You can take multiple pages out and view them side-by-side even if they were written at different times, and are thus separated by a lot of other notes. And so I've kept a very well-organized campaign binder, leaving the laptop at home.
Until I discovered Evernote.
Evernote is an organizational tool that isn't designed specifically for tabletop RPGs, but it works nearly perfectly for it. You create folders, which you can organize into stacks and/or pin to a shortcuts sidebar, and in the folders you keep "notes." A second sidebar lists all of the notes in a folder. Each note can be given multiple tags, but a search bar can make it even easier to find specific things as it searches the body of the notes. You can attach pretty much anything to a note (a spreadsheet, a pdf, a web page), keeping everything at your fingertips. Because that's the real beauty of Evernote. Everything is so accessible with a single click.
As an example, I have a stack for 13th Age. The stack contains 3 folders - a general folder (for big-picture brainstorming that I won't need to reference at the table, and probably isn't related to the current campaign), a folder for my current campaign, and a folder for "set pieces" (generic cinematic scenes that I can adapt to many situations, which is great for on-the-fly encounters). My campaign folder and the set pieces folder are both in the shortcuts bar, so I can switch between them with a click. The campaign folder has a bunch of notes, each with a very specific topic, and all are listed along the side for ease of switching between them. I've got a note with all of the PC information (icons, backgrounds, OUTs, etc.), an NPC list, a list of random names that don't have NPCs attached to them yet, the monster builder reference sheet, a player reference sheet, a GM reference sheet, a list of homebrewed potions, a damage tracker, specific notes on using the icons of my PCs, and of course an individual note for each week's session.
Everything is organized into its own category, and each note is relatively short so you're immediately looking at the exact information you need. Try it. It'll make your GMing life much easier.
On a related note, I decided that since I'll be using the laptop for Evernote, I might as well make a damage-tracker spreadsheet for combat. This is great, because when I'm tracking damage on paper and I have 8 monsters to pay attention to, and multiple players shouting things at me (they're great, really), it sometimes takes me a second to mentally do the math. More importantly, I have to devote my mental energy to doing math as opposed to coming up with cool things for the NPCs to do, or good ways to describe the action. The spreadsheet's great because I just have a column for each monster, and I list its initiative, any conditions, and its total HP. Under that I have a SUM cell, so when a player calls out the damage they did I just type it into the next cell down and the SUM cell spits out the total. It's made things noticeably easier on my end.