If you get over a certain amount of properties, seeing everything horizontally becomes a nuisance.

I install only cheap horizontal blinds because they make the windows look uniform and black appliances are ugly and make the kitchen less bright.

Sometimes people only replace the horizontal pipes because they are the first ones to clog up, and they are much easier to access.Another thing I do is scope the sewer drain.

Almost all new construction is "propiedad horizontal" which means there is a HOA which not only charges sometimes hefty fees (especially if there is a pool and elevators to be maintained) but may prohibit STR at any moment.

Los Angeles is the 2nd most populous region in the United States, yet it is a very horizontal city over reliant on the single family. 

I was quoted ~$7800 for a 1-story 1100 SF house for horizontal vinyl.

That maybe out of state investing to get the cashflow and get to a better place on your horizontal goals (passive income goals), and then look to what you want to do on the vertical goals (active income side).All of that will get you going in the right direction, and see what you could be on the active/passive side of real estate, and making money. 

There may be fire blocks (horizontal 2x4 between the studs inside the wall) that you have to drill through.

In any case, unless you had severe pressure from inside the walls - i.e. if the entire basement was filled with dirt and heavy waterlogged dirt is providing horizontal pressure on your walls - you really don't need virtually any dirt around it at from a structural point of view.

The word "seller" and the line I wrote my signature on are not horizontal.