I am 59 y.o. married man and my wife does not want to cruise so I go alone. I haven't done so yet but I can see mutual benefit to sharing a cabin besides the obvious cost savings. For the woman.
1. Help with luggage & carry-on bags.
2. More safety walking about at ports and on excursions.
3. No dirty looks from women when you talk to their husbands (since you are with a man yourself)
4. A dinner & conversation companion.
5. Having a dance partner (no being asked by men you don't care to dance with or nobody at all) and
6. A platonic friend to spend a little or a lot of time with and no tension or expectations.
For the man it is many of the same advantages plus if you are walking around the port of call and get lost, the woman can ask directions since men never want to.