We’ve had periods with two dogs, then one, then none, and now two again.
When one does you still have another. It’s not as devastating. In fact, with my first dogs, when dog 1 died dog 2 was delighted!
Pros:
If they get on they have a playmate. My current dogs enjoy play fighting, chasing each other round the garden and dry humping each other.
Company if you go out or have to put them in kennels or dog day care
Fun
More dogs for people to play with and cuddle
Cons:
They may hate each other. My first two never got on and it was horrendous. We had to keep them apart when we went out - childgates between the. We had to transport them in separate cars. We couldn’t leave them with anyone else.
Hair, mud, wet dog smell.
People will invite you round with one dog, less so with two.
Harder to find holiday accommodation
They may have different exercise needs. My dogs are 9 and 11. The 9 yo still likes a good hour plus of walking round the fields. The 11 yo can’t do that and needs a very slow trudge around the village. Two walks takes up most of the morning!