Effective to the degree they have a material impact on the economy and psychological impact on the powerful and their lackeys. I would argue many of the BLM protests had an effect, if minor, because many cops quit and many cities still have fewer cops than they did before due to difficulty hiring.
Blocking commerce, looting, and arson of empty buildings have significant economic and psychological impacts. From an American perspective, successful social movements like, the suffragettes, civil rights movement, anti-slavery activists, and workers rights groups all engaged in such strategies. It wasn’t until well after that these movements were sanitized to be “non-violent”.