Going platinum blonde is a big undertaking.
At the very least, you’ll need your roots done every four to six weeks (viaByrdie).
“What you should probably ask is, ‘can my hair handle it?’

‘How often will I need to do my roots?’
Do you think it will look good on me?'”
Many colorists advise trimming your hair after you color it to get to remove damaged ends, as perBuzzFeed.

This is especially true when dyeing your hair very light sincegoing platinum can easily damage your hair.
Also, dyeing your hair platinum is very time-consuming.
You may need a round or two (or possibly more) of bleach but before toner is applied.

Consequently, when your hair is shorter, it will cut down time at the salon considerably.
Not only may you need multiple boxes, but there is thepotential to unknowingly damage your hairbeyond repair.
A professional stylist or colorist can help address issues that may prevent you from getting optimal results.
They can also help make the process less painful (viaGlamour).
On the upside, short hair requires less of everything.