Is using string and rulers really easier or better than a grid?
It's really up to you (especially as it's a system neutral option).
Depending upon the size of the battlefield, rulers, strings, or tape measures might work better for some folks.
For instance, one of our DM's enjoys having large battlefields built in 3D on 4 ft by 8 ft foam boards. He might have several minibattles within a single larger battle all going on at once. If my elf sorcerer with his trusty bow wants to fire a shot at an enemy 3/4's of the way across the board at an angle, it's often quicker to use a tape measure to calculate distance.
Also, he's not a fan of the 1-inch grid. Says it seems too small next to some of the Reaper minis we use. So, gridless works better for him.