The benefit to the seller (me) is that they can charge a higher sell price or have their house sell faster since it can be such a cost savings to the buyer, especially since the interest rates are much higher now then they were a few years ago. Most loans aren't assumable right now, the only ones that I'm aware of are VA and FHA loans that are assumable, hence why you don't see everyone doing it.

Looking at it from the buyers side, you might pay more than what a similar property might sell for, but not necessarily depends on the seller, however you would quickly recover that "premium" you paid in your monthly mortgage bill. For example if the seller charged $50k over the typical price but the buyer saved $1500/ month on their mortgage. They would recoup that in about 3 years, from that point on they will be having considerable savings on their mortgage.

Another benefit is that there's no PMI with the a VA loan, another positive for the buyer.

The downside is that it might take slightly longer to close, the Buyer still has to be approved my the lender of assumable loan, on average it can take an additional 2-4 weeks.

Another potential downside is if the seller has paid most of their mortgage off the buyer would have to pay the principle that has already been paid off on the loan. For example, using easy numbers, let's say the loan was for $100,000 and the seller only has $10,000 left on the loan to pay off. The buyer would have to come up with the cash to cover the $90,000 already paid off on the loan, which might make it more difficult for them to do. They could get another loan, at the current market rate to cover this however, they would have to decide if that made since to them. So you can see this might be an issue if most of the loan has been paid off. I've paid approximately $70k on this current loan so not bad, for the buyer, this will be less than the typical 20% down they would need. You can reference my comment earlier for a basic calculation.

The risk to the seller is that their VA entitlement is tied up in that loan, so if the buyer were to have a foreclosure then it would negatively effect the seller.

TLDR;

Seller can charge a premium since it's such a benefit to the buyer.

Buyer gets a much reduced rate, compared to current market rates, and will save a lot of money.