The GRE-optional wave was supposed to be temporary. So why is it still here? Because it works for schools, and mostly it works for applicants too. The list of universities that waived gre requirement policies keeps growing, and plenty are keeping the change.
The upside is obvious. No test, no prep, no fees, no bad score following your file around. If standardized tests were never your thing, this is your window. Programs are putting real weight on the SOP, the recommendations, the projects.
But do not read "optional" as "irrelevant." Plenty of departments still quietly prefer applicants who submit strong scores. A 168 quant on an optional application is a loud signal. It says: I could have skipped this, and I proved myself anyway. If you test well, submit. Silence invites assumptions, and assumptions rarely favor you.
Then there is the gre vs gmat which is better for ms admission question. For a straight MS, the GRE is the default. The GMAT is for business school. Some management-adjacent programs take both. Check each program's stated preference, because a GMAT score at a GRE-focused engineering department just confuses the reader.
My advice is boring and correct: build the list in two columns. Test-optional schools where your profile shines without scores. Schools where a strong GRE makes you stand out. Do not go test-optional everywhere out of laziness, and do not take the test if the hours are better spent elsewhere.
One more thing. When the GRE disappears, the SOP carries more of the weight. Check a GPA and test score requirement database by program to see the average gre scores of admitted students by program anyway, it tells you what you are competing against. Then get the essay shaped around each target school. The tailoring packs at sopexpert.fyi build it around your actual schools.