For the first time, my home PC has no expansion cards
When I started out with PCs, you needed a bunch of expansion cards to make them do anything particularly useful. In the era of my first home PC, almost all I used on the motherboard was the CPU and the memory; graphics, sound, Ethernet (if applicable to you), and even a good disk controller were add-on cards. As a result, selecting a motherboard often involved carefully counting how many slots you got and what types they were, to make sure you had enough for what you needed to add.
(Yes, in my first PC I was determined enough to use SCSI instead of IDE. It ran BSDi, and that was one of the recommendations for well supported hardware that would work nicely.)
Bit by bit, that's changed. In the early 00s, things started moving on to the motherboard, starting (I believe) with basic sound (although that didn't always work out for Linux people like me; as late as 2011 I was having to use a separate sound card to get things working). When decent SATA appeared on motherboards it stopped being worth having a separate disk controller card, and eventually the motherboard makers started including not just Ethernet but even decent Ethernet chipsets. Still, in my 2011 home machine I turned to a separate graphics card for various reasons.
With my new home machine, I've taken the final step on this path. Since I'm using the Intel onboard graphics, I no longer need even a separate graphics card and now have absolutely no cards in the machine; everything is on the motherboard. It's sometimes an odd feeling to look at the back of my case and see all of the case's slot covers still in place.
(My new work machine still needs a graphics card and that somehow feels much more normal and proper, especially as I've also added an Ethernet card to it so that I have a second Ethernet port for sysadmin reasons.)
I think one of the reasons that having no expansion cards feels odd to me is that for a long time having an all-onboard machine was a sign that you'd bought a closed box prebuilt PC from a vendor like Dell or HP (and were stuck with whatever options they'd bundled in to the box). These prebuilt PCs have historically not been a great choice for people who wanted to run Linux, especially picky people like me who want unusual things, and I've had the folkloric impression that they were somewhat cheaply put together and not up to the quality standards of a (more expensive) machine you'd select yourself.
As a side note, I do wonder about the business side of how all of this came about. Integrating sound and Ethernet and so on on motherboards isn't completely free (if nothing else, the extra physical connectors cost something), so the motherboard vendors had to have a motivation. Perhaps it was just the cut-throat competition that pushed them to offering more things on the board in order to make themselves more attractive.
(I also wonder what will be the next thing to become pervasive on motherboards. Wireless networking is one possibility, since it's already on higher end motherboards, and perhaps BlueTooth. But it also feels like we're hitting the limits of what can be pulled on to motherboards or added.)