chemicalscleaningpaintingsanding
White spirit (aka mineral spirits or mineral turps in the US), methylated spirits (aka denatured alcohol in the US), and isopropyl alcohol are each used for preparing surfaces, or removing oily residues.
Other than 'whichever is to hand' or 'the cheapest', is there any reason to prefer one over the other for this application?
If you're talking about tools like this, then you can use them vertically.
The manual for the tool I linked to doesn't have any mention of the words horizontal, vertical, level, flat or upright, so if they don't warn you not to, you can assume it's OK to do it.
One thing to note is that to sand a vertical surface, you're going to have to hold the tool more tightly than you would if you were working on a horizontal surface. This will cause more vibration to be transferred to your hand and wrists, which will tire them out more quickly. If you're doing a large area, this can cause repetitive strain injury; when I sanded some window frames a while back, it took a couple of days afterwards for my wrist to feel OK again.
If you are cleaning something that can be washed, you can neutralize the pH with water. After using HCl on bricks, I would just hose them off. The acid will become very dilute quickly. pH just measures the concentration of hydrogen ions in a solution, so if you add a bunch of water (neutral pH) the pH will approach neutral.
I also don't think you need to worry about the pH of solids such as dried plaster.
Best Answer
You need to match the solvent to the type of material you trying to remove. Fundamentally there are polar and nonpolar molecules. Water and denatured alcohol are polar and mineral spirits is nonpolar. Oils are nonpolar, which is why oil and water don't mix. So to clean up an oily surface, you need mineral spirits. Somehow some dishwashing liquids also work (like Dawn).
YES...I know there is a LOT more to this subject, but just trying to answer the OP's question without going overboard.