Stairs... why 2 choices

[大树]

Why would you build normal stairs where I feel spiral takes less space and you can connect all levels.

[Rany Rarks]

First point I would like to say is Stairs can be used to build diagonal access between rooms, as Stairs can be built passing through walls.
Second point is that the Z-axis of Stairs and Spiral are different. Depending on your room structure and setups, Stairs can be useful during your design.
Hopefully someone can have creative examples to illustrate more Stairs features lol

[robbie.price]

Also eventually you get ladders, which decrease luxury, but take one tile against a wall, and I took out the spiral staircases after that.

[Isenfalk]

Spiral and normal stairs have both upsides and downsides

Spiral stairs take less overal space, but they are in the must be placed in the middle/front of the space, removing space for furniture, which is limited in the early part or the game.

Normal stairs need more overall space, but they always hug the back wall, so you can have both stairs and furniture in the same space.

[Stranger]

You can also use stairs to have a room that has a step up, or uneven floor with a single tile of stairs, its nice when you play around with it.

[Havok]

I don't have access to my builds from beta sadly, but I used two types of stairs for more creative architecture, as in different floor levels and extra "hidden" passages between the areas of my tower. I wish they added like stone cobbled floors so you can have flat roofs that the characters can walk on to access different areas across the rooftop and stuff.