BTC is an investment itself, so putting money in is always good... Don't turn to burning massively, but the extent to try some is always worth it if gains continue.
Don't forget that the need to diversify is sufficient, so always reserve your fiat.
yes nowadays bitcoin holding is a good source of investment if someone will wait for a longer time with their money and will not spend them or sell them then they will earn a good income when the price of bitcoin will rise in the future.
It is like all other investments, but the only difference is bitcoins prices can fluctuate faster than other investments. I usually don't keep all my bitcoins for future appreciation instead only around 25% of bitcoins keep it for longer term appreciation and remaining will sell when I reach my target profit percentage and again I will buy if prices reach my buy target.