Yeah...it's mostly for the satisfaction and pride of being one that's beaten the two weapons of FF7 If you want a short general guide to what I did (this strategy worked best for me, but there's different ones you can find online):

(SPOILER)
For Ruby, I would actually use the W-summon materia to summon Knights of the Round twice (I personally like to link it to an HP absorb materia as well), or if you can't do it twice...do Hades once, and KOTR once. Keep using the Mime materia to mime it. You can equip Final Attack materia with Phoenix...but if you die I would just restart as it'll be hard to beat once you've lost the ability to mime KOTR.

For Emerald, definitely get the Underwater materia to get rid of that time limit. Similar strategy to above.

If I recall correctly, you get stuff for beating the weapons from the Kalm Traveler quest. I don't know if you want me to tell you what you'd get so: (SPOILER)Gold Chocobo and Master materias