inactive vs active partitions help

So I know this much, Active partitions are the partitions you boot from. What are the reasons you would mark a partition as inactive? Every google response comes up with "how" to mark them but i want to know why i would mark them.

I have an SSD with my OS and three HDDs. HDD #1 is a 1 TB Hitachi HDS721010CLA332 that i split into partition A: Temp Files and downloads (200gb) and partition B: My working files where i store everything im currently working on. (Word docs, Excel Sheets, MS OneNote, unfinished projects, games that dont need to be on the SSD, MP3s, photos that need to be organized) HDD #2 is a 1 TB Hitachi HDT721010SLA360 that i use primarily as storage/backup for all my files and ISOs of programs and partitioned accordingly. HDD #3 is a 5 TB Seagate ST5000DM000 that I use as a media drive.

Am i categorizing things incorrectly? Anyway all four drives are marked as primary and active, and it just seems like I should be marking all my HDDs as inactive and as a logical drive (or is that only one MBRs) I dont want my storage drives to have any outside access without me physically moving items from storage to the working HDD and i dont want to use external drives. My seagate drive will soon be transferred to a home media server. Am i barking up the wrong tree?

Please advise.