Migrations are when metadata problems surface all at once. Descriptions written by six people over four years, some auto-generated, some copied between pages, all about to be carried onto a new platform without review.
Running the check first
Measure the whole set before migrating anything. The output splits into three actionable piles: over the limit and truncating, far under and wasting space, and identical to another page.
Deal with the duplicates first
Duplicated descriptions are the worst of the three. They usually mean a template is generating the same text across a whole section, which tells searchers nothing about why one page differs from another. That is a template fix, and fixing it once resolves hundreds of pages.
Then prioritise by traffic
Do not rewrite four hundred descriptions by hand. Sort the problem set by the traffic each page actually receives and rewrite the top fifty properly. The rest can wait for a template default that is at least accurate.
Try it: Meta Description Length Checker on SeoWolf's Notepad.