Letter of Rec from HYPSM professor

Hi, I don’t want to reveal too many details since this is quite rare, but I’ve been working one on one with a well-established HYPSM professor. They are well-known and have a high H-index. They are extremely impressed with my work and are willing to write a letter of recommendation. Is this significant and would it bear a lot of weight?

It’ll obviously be a positive, but as with your other thread, it depends on the school you’re applying to. If its an ivy/T20 (not the one the professor is from), it won’t bear as much weight since other applicants will probably have stellar recs from professors they’ve worked with.