I had a VM with a swap partition that I deleted. I now have two primary partitions sda1 and sda2, both ext4. In windows they would be seen as separate drives, but how does linux use these 2 partitions vs one large sda1? My searches just end up talking about how to make partitions or about advantages of partitions. 
How is sda1 used differently from sda2?
partition
In practice, they will effectively be used as two separate drives by default, much like in Windows, as you state. For example, if /dev/sda1 has 50MB free and /dev/sda2 has 50MB free and you try to write a 75MB file to either, it will fail with a disk full error despite both of these partitions being divisions of the same disk. 