Grid for maths has been used for well over 70 years. Don't think it serves much purpose. Except for graphing, I do not use grid book for maths. Also hard to read written words on grid. That's how I feel about it anyway.
Think of it like this: (This is what I noticed in my school)
Grids, for people who do general mths and are recommended for them. Why? Less theory
Lined, people who generall go over general and do 2u+, better for writing theory and working outs, it turns out to be neater and more elegant too ^^. I recommend this more
Generally I see people using Lined more than grids nowadays, anyway I got a spare Gridbook just to do practice as it makes graph drawing faster imo