Are drink coasters for people who frequently spill their drink or have trouble drinking without dribbling down the cup?

They're to prevent condensation from pooling on the table itself. This can warp or otherwise mess up a wooden surface. On other materials it can just leave ugly rings that you have to clean off.

Also to prevent hot drinks effecting the surface finish of said table via temperature effects etc.
Question, my table's wood edge is warped from my fore arm sweat. Wtf can i do beside replacing everything
- Not a lot. You could try planing the edges to make it look even, but that would also mean having to stain/treat the wood after. Trying to get it to match would be a challenge.
- Arm coasters.
- Plane or sand it smooth and refinish it. Probably you would need to strip and refinish the whole thing to blend it in but that is an advantage to wooden furniture.
- Wear sleeves

Condensation. if wooden tables get exposed to it over time it ruins the wood/leaves stains

This is true for cold liquids. Coasters are also good for hot liquids in a cup. These can also damage a surface.
Theoretically if you had a room temperature drink in a cup you would not need a coaster.

In addition to the condensation, I have also used coasters for under hot drinks like coffee as they can discolor or even deform some surfaces.

If all you drink is room temp liquids you don't need coasters.

They are to prevent condensation from damaging the surface beneath them.

You have to respect the wood.

I respect wood. I revere wood. I’m considerate of wood.

It depends on the humidity of where you're at. On a warm day in Houston, for example, it's not at all uncommon for water to condense on the outside glass of a cold drink, run down, and eventually damage the wooden table it's sitting on. A coaster will help prevent that damage.

Ever have your coaster stick to your glass or cup. Follow this trick! Shake some salt on the coaster. It will never stick!

Got it. So what's the order. Lick coaster drink shot of tequila bite lime? Or bite lime, drink tequila shot then lick coaster.
- Bite coaster, pour tequila in sink, add lime to taste.

Additionally to what else was said, I've seen them used in beergardens to cover the drink to prevent bugs from drowning themselves in your drink. I guess then the coasters don't serve to protect the table anymore.

That's the possibly apocryphal origin story of Spanish tapas, too: a slice of bread to cover the wine glass between sips (hence the name "tapa," which means a "cover"), then a few things to dress up that slice of bread, maybe a piece of meat or cheese. So traditionally a single tapa is served for each glass of wine you order.
- I didn't even think about the German word, which is Bierdeckel - literally beer cover. Well the boring word for it would be Untersetzer, which is the substantive of "to place underneath".

Every mother always insists in using coasters and makes sure to explain to you a millions times why is that and will burn the house down if they find a cup mark.

"Listen honey, mommy raised you pretty much on her own because the patriarchy normalized men not contributing to the nurture of their family, and now mommy is one ring stain away from a total mental breakdown complete with arson, okay?"

Nah, they're so your wine bottles can coast on tables.

Seriously, that's what they started as.

Using them to protect tables came later

Works best with an air hockey table.
- Is there another kind of table?

Try thirsty stone coasters. I found a really large thirsty stone trivet which I use. Combine with tervis tumbler for the ultimate drinking setup. Lol. For spilling; try a straw. Or try a baby sippy cup?

Sippy cup? I am a manly masculine man, I drink from a teapot!
Hipsters, pfffft...