No question about it, that makes perfect, logical sense. Why spend anywhere from $300 to $800, or more, for a standalone GPS when you can add the same capability (or close to it, anyway) to a laptop for $100? Any and all arguments that people make for using a laptop instead of a standalone GPS I have emphatically made myself. I know where you're coming from. Absolutely.
In addition to the economics, with me being a mad computer geek, a standalone was never an option. It was silly to even consider it. I used my laptop for more than two years out here. But, I found that unless it's on your lap, it cannot handle the bumps and vibrations of a moving vehicle very well. It wears on the hard drive, port connections and a few other internal components.
But the main thing is safety. You need the laptop the most at the very time you can least afford to divert attention from the road. Like, when there are complicated turns or multiple turns in quick succession, that's when you need to focus on the driving, instead of diverting your eyes from the road and focusing on a small spot on the screen, then back to the road. It's not like glancing a few times at a mirror, the laptop screen requires more concentration than that. And making changes to the route or otherwise fiddling with the laptop while driving is insane, even though I used to do it, too. You wouldn't even consider putting the newspaper on the passenger's seat and then try to read it while driving, but whether you admit it or not, that's what you're doing while using a laptop while driving.
I know of two people in this business who have had accidents while tending to their laptop, and a third driver, well, that's only speculation, as we'll never know for sure about that one. Be that as it may, I won't tell anyone straight up to not use a laptop, as I used one for a long time. I only say strongly consider what you're doing, and how and when you're doing things with it, then strongly consider using a thing for it's purpose. A laptop as a laptop, a GPS unit as a GPS unit. $300 or $400 will seem like an awfully small amount of extra money if you rear end or sideswipe someone because you had your attention diverted from the road for a scant few seconds.
And even after all that, I do still carry my USB GPS receiver to use with my laptop as a backup.