Steem Monsters Question: Should you combine all your cards or keep them as singles?

Hey guys, I was just wondering... is there an advantage or disadvantage to combining all your cards? I know this levels the card up but does that only make the card worth more? Does leveling a card up to it's max make it more battle-strong?

I didn't think the stats change on a card as it levels up but I could use a solid answer here...

Not sure whether I should just collect a ton of the same card or if I should combine them all to the max as much as I can...

Any thoughts?