It all depends on your trading style.
If you're a day trader, it's a must and something you have to do every time you enter a trade (stop loss).
If you're an investor and your goal is just to increase your coins, then I don't think you have to put a stop loss. After all, if you don't plan to sell a conventional BTC for 10 years, you may reinvest a huge amount of times during that time!

I think it is very risky and generally not worth borrowing money to invest, because in the end you have no control over anything and even if you think that the idea is 100% correct and now it will be TO THE MOON, it is only your opinion and the chance to be wrong in such a case is really huge!
I think that if you don't have a big amount to invest at one time, you should do it every month, but in small amounts.
I do it that way and am very satisfied. I don't really care about the price, because I'm investing for the long term and every month I buy coins, thus accumulating my asset.