And the other "local" wallets takes the same GBs from your hard drive? And where in my hard is stored this data (from Bitcoin-Qt sync)? I tried to find it but w/o any success, because if I would like to remove this wallet there will be a lot of space gone somewhere.
C:/Users/*username*/AppData/Roaming/Bitcoin
Your wallet.dat is also stored there.
If you don't have any money and don't want to use bitcoin-QT client delete it.
You can use online wallets or light weight clients like electrum.