What are the virtues of disc brakes?

and disc breaks screech unless you maintain them regular, very unpleasant sound lol.

I was a mountain bike user for 2 years and loved my disc brakes, when I got my first road bike I swear to myself my next road bike would have disc breaks but now I love my break blocks I feel I have more control over my breaking, the disc breaks are very good at stopping you suddenly something that is needed on a mountain bike, not as necessary on a road bike, but that is just a personal point of view.

You need a new frame and fork or a new bike, I wonder why the manufacturers are pushing this !!

just to add to the mix, the downsides.

Discs do rub, how ever you set them up you find the odd ping ping noise.

Inserting wheels can be a real ball ache, the gap between the pads isn't great, it is very easy to insert the wheel with the rotor trying to go behind the pads. This is far worse for the back wheel where your also fighting chain and rear mech.

Disc pads do where out, and some rotor pad mixes wear extremely fast!

Banshee like howling!!! if you thought squealing callipers was bad, wait till you have a set of disc brakes that want to squeal!

This is from my experience of running discs for the last 5-6years on the MTB. Whilst there are benefits on the road, there are downsides, would i use discs, well i suspect my next road bike will have discs because that will be what is available, would i buy a new bike to get discs? no.

Reliable and very easy to maintain.

If I could put discs on my road bike, I would.

Though much care and ingenuity have gone into the development of callipers and pads, the rim brake is fundamentally a flawed idea. Maintaining the structural integrity of the wheel under the loads imposed by spokes, tyre pressure and potholes is the rim's primary task: grabbing it to slow down is an afterthought. The rim wears (even with Salmon pink pads) - until it fails. And physics and Sod's Law agree that it will fail under maximum load - ie when you hit a pothole hard or slam on the anchors just before the hairpin.

And when the rim fails the wheel collapses.

(OK this is all a bit melodramatic but it does highlight the main reason for disc brakes, in my opinion.)

You can't upgrade to disc brakes unless your frame has bolts for the callipers. The fork also needs to be stronger which means you get less flex.

Anyway not sure I see the point on road bike tyres, if you can pull a skid you have as much stopping power as you can use. With decent pads callipers are fine in winter on a road bike. I had discs on the last bike and they were great but I had 32mm touring tyres and panniers so could jam the brakes without skidding or the back wheel lifting. The only time I've had an issue with callipers is during really wet weather and riding through puddles that must have been full of diesel or oil. The rim gets covered and it takes a full revolution to clean the rim. I just ride a little slower in the wet and leave bigger gaps.

'cable stretch' isn't actually the cable stretching, it's just the ferrules and such settling into their locations properly. once that happens things generally stay as they are.

I think "cable stretch" is overemphasised by people with something to sell. My old Ducati motorcycle had cable operated brakes, and I never had any problems.

Are they heavy? Yeah but only a tad heavier than u-brakes or v-brakes. You won't notice the weight change unless you have a featherweight bike.
Are they easy to clean/maintain? Yes you only have to change the pads once every 8 months to a year. Other than that, they self adjust as they wear and are fully enclosed in the caliper so never get dirty/wet..
Is there more stopping power? Yes. When you have a cable system the cable will always stretch a little when pulling the lever thus taking away some of your power. Hydraulic systems use mineral or dot fluid which compresses the pads against the disc. Whichever you use you will not have that issue..
They can only be damaged in a serious crash. They are as likely to take an impact as your cassette..
Hope this helps you.

It's about reliable stopping power, whatever the conditions, I think. It adds a bit of weight but you're not affected by road gunk on your rims. Your brake pads won't wear out as fast, and rims won't be subject to wear.

I'll definitely consider discs next time I get a new winter bike.