Your practice of waiting until you can pay cash is a good one. It will certainly prevent you from getting into debt!
Now, to be clear, your question puts a credit card in the same category as a loan, but it doesn't have to be. You could use a credit card almost like cash, if you are careful.
I'm not familiar with the system in France, but in the US, even if you are paying cash all the time, there are some benefits to getting a credit card and paying it off in full every month, instead of simply paying with cash. Some of those benefits are:
- You get to wait 20-30 days before paying for the items.
- You will start to build a credit history, which in the US is helpful when you want to borrow money in the future. [Note: The concept of credit building currently doesn't exist in France. Thank you @Relaxed for mentioning it.]
- You don't have to carry as much cash around with you. If you lose your wallet you can cancel your credit card and get a new number.
- Some credit cards allow you to earn "points", "airline miles", or even cash back on every purchase. Typically the value of these incentives ranges from 1-2% of the purchase price and it is basically free money (when compared to paying cash). [Thank you @apsillers for reminding me of this.]
One pretty big downside of having a credit card depends on your personality. Some people, once they have credit, end up spending beyond their means, and end up getting into debt.
Please look into whether credit cards work the same way in France before considering the above advice.
As for your question regarding getting a loan vs paying cash, that will usually be personal preference, since with a loan you can buy expensive items (such as a house or car) much sooner than you otherwise could if you waited until you saved the money. For example, it might take 10 years or more to build up enough money to purchase a house with cash, so if you don't want to wait that long, you'll need to finance it.