Also note that some VPNs can compress data (only data that is not already compressed or encrypted - like plaintext HTTP, IMAP, NNTP or SMTP traffic; but not HTTPS, TLS, HTTP+gzip etc.), which might also make traffic somewhat smaller. For example OpenVPN can use
comp-lzo option to compress data if enabled on both sides. So you can't hide that you've transferred data, but in some cases you could transfer less data that you would without VPN.