When it comes to developers, and using a dilution to increase yield and/or reduce waste, does it effect the print any?

When I use my Arista, I was doing the suggested mfg. mix. 1 part developer to 9 parts water and was developing for 2 minutes. Since I don't print much, I've decided to go 1:2 and go 4 minutes. I can't really tell a difference, but is there in the grand scheme of things?

TIA