although its not mandatory, its HIGHLY recommended, it cuts plegm use from mining ore block in half 5 phlegm per instead of 10, it aslo chips at 30% per chop instead of 15 (shovel) it is expensive , but if your using it for mining then your producing bars anyhow, so 3 bars isnt so bad! id suggest getting it, it will cut your lime chopping/rock chopping/ ore chopping times in half.
Yeah I just made my first pickaxe today and am loving it already! Didn't know that it will be that much faster. And I really like the fact, that it also speeds up lime and stone chipping!