Yeah, the peace of mind was a big factor. I remember the entire time I was buying the water from my LFS I was stressed out beyond belief trying to get my tank right.It’s not guaranteed to be the correct salinity. It’s not guaranteed that they change their filters as often as they should and that their water is 0 tds. Personally, I just don’t trust any LFS enough to handle such an important and integral part of a successful reef. It’s cheaper, by far, to make your own water. There is an initial expense, but a gallon of homemade RODI water costs around $0.05, salt can be anywhere from $0.20 to $0.60 per gallon, so for 5 gallon at most it’s going to cost you $3.25 (or as little as $1.25), compared to $10, for RODI it’s $0.25 vs $5.00 for 5 gallons. And not to get too cliché, but the peace of mind is priceless.
It's best to know you started off with water you make on your own that you know for a fact is pure 0 TDS. Knowing what your parameters are because you made the mix yourself I think will help with your coral too. Whether you might need to add a little something extra to the tank if the salt you have doesn't match what you want exactly.
I just love having as much control of my tank as possible and this is a really big one.