A MimbleWimble design is good for pruning. If you are familiar with UTXO model in Bitcoin this can be explained in comparison. A transaction in Grin contains outputs and a kernel which is a signature. Spent outputs can be pruned from the blockchain. Kernels cannot be prunned, but all the transaction inputs are signed with one signature. With all above, grin should use storage more efficiently than bitcoin. Don’t know exactly, maybe 3-5 or more times depending on actual utilization.

Currently the grin node uses about 1GB with pruned blockchain, it is 1/3 of all the historic data: https://grin.blockscan.com/chartsync/syncarchive