2.5" SSDs are dense enough and cheap enough now that it makes sense to replace 2.5" HDDs. I have been using a M.2 NVMe SSD in this laptop for GNU+Linux, but I still had Windows on the original hard drive. However, whenever I had to boot into Windows, I was reminded just how slow Windows and hard drives are.
Before
The old hard drive weighed in at 89 grams. The new SSD weighed 38 grams, less than half the weight.
After
The real savings should be in power and response times. I tested that Windows still boots, and it only took several seconds. I did not measure the boot times, but it seemed much faster. Time will tell.