My son-in-law is in the business in the Hartford area. He cannot do my DE drive (too far) but has told me what to get and look for.
Crack filling is important. Nothing you can pour (crack filler in a 1 gallon container) will work. The stuff you buy, force in the cracks and heat with a torch may work. The professionals use hot liquid rubber. It's usually in a push cart and kept hot by heat from a propane tank. The better machine is on a trailer and has a boom with a hose that pushes out the hot rubber. That machine is $50K. Even professionally filled cracks may come back as there was a reason it cracked in the first place.
As far as sealing, it makes it look better, protects against oil or gas spills and hopefully seals hairline cracks so they do not get larger.
The gypsy rip off people use Gilsonite and thin with diesel fuel. If it needs to be thinned they should use mineral spirits (I think,). Not diesel. Gilsonite leaves a very shinny surface when it dries. I do not think it does a great job of sealing.
Most places use coal tar driveway sealer. It does a good job and lasts a good period of time, BUT the dust produced as it wears gets into your house and some into ponds. It's pretty nasty dust from and environmental and health perspective. Many states ban it.
The best sealer in my opinion is an asphalt emulsion sealer. It's expensive. You will probably not find it at Lowe's or Home Depot and may have to look hard for a company that can deal using this.
The cold call people who say they have left over sealer probably use Gilsonite. Thinned with diesel or not, I do not think it does a good job.
All companies fill there tanks every few days so they always have some left in their tank. It's time consuming to drive and get the tank filled so that is why they typically have a tank that can last several days. My son-in-law has a 12,000
gallon tank as his shop that gets filled once or twice a year.
HomeDepot sells an Epoxy based driveway sealer that I am trying.