I don't know to be honest. My Ob-Gyn recommended every other day - he said sperm can stay in your system for up to 5 days anyway, so doing it every other day means you'll always have sperm in your system during ovulation and that it might be 'stronger sperm'
as you're giving it more time to 'recover/rebuild' if you leave it every other day.
In the end, we compromised and did it every 36 hours (so one night and then the morning of the day after that, then the night of the next day etc etc iyswim)
It worked for us, eventually!
I know others who prefer to cover all bases and just do it every day, but according to my doctor, it's not necessary to.