We're traveling internationally as a couple and are allowed 2 pieces of checked in luggage. Is it OK to send 1 slightly overweight piece instead of 2 underweight pieces?
Edit: flying El Al
Take two suitcases. You will (probably) get charged extra for the overweight bag, and if it's too overweight they won't accept it at all. And you will pay again on the return.
Assuming you are going on vacation, you will most likely buy something and need a way to carry it home. yes? One overweight, stuffed to capacity case won't work.
Note that a completely empty case is often a problem too - it's so light it doesn't go through the baggage system well and can get blown off carts when outside.
Overweight bags are not only so designated as a way to make money for the airline . They can actually be difficult for baggage handlers to, well, handle, and to place inside the hold etc. The extra fee is to deter you from bringing a heavy bag; the airline would definitely prefer even a single traveller to bring two lighter bags.
Then to complicate matters you're hoping to combine baggage allowances in order to do something the airline would rather you didn't do? I bet that won't work out well.
Bringing two bags will give you a sort of insurance against baggage delay or loss - put a mixture of possessions in each bag. It will also save you struggling with a very heavy bag for the parts of the journey where you have to handle the luggage yourself. If the issue is that only one of you can handle luggage, then find a way to connect the two bags so they can be handled as a unit. Check Travelling with 2 check-in bags for more on that.
What finally happened was that they let me on with 2.5KG overweight - 25.5KG vs 23KG advertised limit. I didn't ask too many questions, and this isn't the first time I got on with overweight luggage to an El Al flight. Note that 25.5KG is still well below the limit for business class luggage.
Of course - your millage may vary.