www.makemkv.com

is there any advantage of buying bluray disk and playing on pc over streaming services like amazon prime in terms of video quality? or both offer exactly the same quality?

Blurays are much higher quality on streaming services your lucky to get a bitrate of 15Mbps
regular blurays are at least double that and UHD bluray can peak over 100Mbps

To echo what Billycar11 said… if you buy a movie on iTunes (or whatever) and download it, you'll end up with a file around 5GB. That same movie ripped from a blu-ray will be about 30GB.

thanks for clarification