Right now you do not need to buy fast since the market is currently low but it was the good time to invest a huge amount in order to earn more profit when the market goes back to normal.
If you determine this is a good time to invest in bulk, you need to buy fast. Because the bitcoin price on the market is likely to increase around $1000 or $2000 very quickly.
Who knows where the BTC price will move to. You can buy the first "dip", and then the price will drop and you will need to buy the second "dip" and so on.
Although I suppose that the current BTC price is attractive for investments. A few days ago all the top altcoins have been sharply dumped below their support levels, but Bitcoin is on the level $6400 and looks better than them.
In most of the cases trading is more profitable than the HODL tactics, so I can advice to buy a promising coin fast on the low levels and sell fast on the high levels, because the price is very volatile.