I have two older 2.5" laptop drives as imaging/backup drives in my desktop since I didn't know what else to use them for. Once I did an OS image on of those HDd, and there I could clearly see the difference between my OS on SSD and running off a laptop HD. It was PAINFUL. While "booting onto desktop" (until the desktop appeared) was still halfway tolerable...the drives just wouldn't stop spinning and accessing after the boot with loading the AV software and the few startup programs.
I also see this at the wife's LT how disk accesses happen even AFTER the desktop is already visible....in others words the booting DOES take significantly longer until the system entirely loaded all the crap. While it's not "instant" here on a SSD, booting IS faster and it only takes a very short time afterwards 'til disk accesses stop.
This WAS the biggest issue I had with this laptop. Desktop would load and it would still take 1 or 2 minutes before I could really do anything while the HDD spent its time loading auxillary services into memory. I can honestly say that has been reduced to less than 10 seconds. I am impressed by this.
My desktop, by comparison, has never had this issue with platters or I would strongly consider an SSD for it.