It's a depends question. I'm unsure what you mean by lack of space?
You generally can't upgrade the internal components of a laptop except memory and hard drive but when it comes to upgrading the gaming performance, if the in built graphics becomes too dated or isn't designed for gaming, provided that whatever laptop is bought, has thunderbolt 3, an EGPU solution is likely possible. This essentially provides the means for a desktop GPU to be used via an external box connected via thunderbolt 3 capable USB-C ports. Of course that takes away from the portability aspect and increases your footprint.
I bought a gaming laptop a few months ago a Gigabyte P57V7 with 16GB Ram, 8GB VRAM on the in built GTX 1070, 17" screen.
I bought it as a replacement for my tower gaming machine with the biggest advantage being ease of setup and being able to move into another room easily. It's perfect for that. I have a Lenovo Yoga for travelling.
There are several disadvantages of a gaming laptop relative to a gaming PC.
1. Cost and bang for buck. If the bang is gaming performance, then laptops always offer less bang for the buck.
2. Proprietry parts. If something fails, Cost to repair is far more expensive due to the "all in one" concept and proprietry components. I can't just go and buy another mainboard from the local PC store if the one I have packs it in.
3. Footprint. - My desktop tower was on the floor next to my Desk, cables went to the dual monitors, my keyboard and mouse. Additional space on the desk is required to accommodate the footprint of a 17 inch laptop as well as the space around it so airflow isn't restricted now.
4. Connectivity - I only have mini display port out and HDMI out on my Laptop and because it's a dual Video card setup(switches from intel HD graphics to GTX 1070, getting multi monitor support to work seamlessly is at times a bit frustrating and I cannot for the life of me get 4K HDR to work with it on my TV despite both PS4 Pro and XBONEX working ok.
5. Easier to steal
6. in built panels tend to be sub par for gaming although high end ones are pretty decent.
Disadvantages of gaming desktop.
1. Needs to be connected to external monitor with suitable cables as well as external mouse and keyboard.
2. Not portable
3. Doesn't come standard with battery power.
For me - there is value in the ability to physically move my gaming rig to another location in the home very easily. I don't even need to shut it down. One application where portability within the home is is useful for me is the HTC Vive is far better in my loungeroom than the far more restrictive space of my study.
