You end with better control doing 50% vs say 25% 2x a week.
This is due to the remainder being 75% vs 50%, so mixing of the old, with the new does not act like a linear response, it is non linear, so 25% x 2 = about 38-40%, not 50%. 50% change, is obviously 50%, but you lose some when you do 2x 25% etc.
1/3 water changes 2x a week will come closer to being the same as 50%.
If you gain skill and use lower light, good CO2/current etc, you can slowly reduce the dosing down till you note a negative response in plant growth, then bump back to the next highest dosing level. Then reduce the water change frequency and or %. Many do this.
Regards,
Tom Barr