I dabble in GBTC because I can trade it in IRA and the realized gains are not taxable (that is, until I take $$ from the account).
If i can simplify @fillipone's great thread it would be that I invest in GBTC to "gorge" on the increased premium during the bull run.
During the last bull market premium topped 100% at least a couple of times.
If something similar would happen again, it would outperform btc in $$ terms.
That said, it's not a major position for me.