For speculation? To buy on the dark web? To buy online on sites like purse.io? To send money? To do business? To have your money under your control?
What is/are your purposes when yu buy bitcoin?
i buy them usually when i want to play with them, because i really like to use them, so easy to send money, and i also buy them before important bitcoin events like halving, because if i buy bitcoins now, i am sure that i'll can sell them for more after event, it is always nice to make extra easy money, no work needed