The longer the period you keep your bitcoins, the bigger profit, so it should be in practice. But it's not always so and depends also how long is that period. I think too long period is not good, it's better to set some goal within a year or two and try to achieve that otherwise you might get completely lost in calculation and maybe end with loss, not profit.
The longer you hold it the richer you get, that’s the simple rule with obviously no complications involved. Bitcoin is expected to reach to $3000 in the mid-2018 and of course more after that.
So, if you hold it you are definitely earning profit. But if you want to invest it in trading businesses online or online casinos like many people do, you may get double the bitcoins you had, at the end of the day. But of course if you are happy with what you got and don’t want any urgent money it’s best to hold on to your bitcoins.