Do you build your character around your stat rolls, or decide what you want to play and THEN roll? Depends. In 5e I definitely start with a concept and then build stats (with array or point buy) to fit.
In a system like 3d6 in order stats, well, my advice is don't get attached to an idea until you see what you can actually manage.
— Dan Dillon 👥 (@Dan_Dillon_1) July 17, 2019
¿Porque no los dos?
Options exist to suit the needs of the player. One size does not fit all, and even when wielding a hammer not every problem need be a nail.
Sometimes operating under strong restrictions can inspire creativity that otherwise would not arise. Other times, those same strong restrictions can be stifling and smothering, causing a player to feel frustrated and uninvested.
I think most players prefer devising a concept first and then rolling, because it gives them far more freedom to make a character they know they will enjoy, but at the same time I recommend to anyone even remotely interested that they at least once try rolling first and then working to devise a concept that suits the stats, and see where the experiment takes them.
Some players will find the limitations prompt them to arrive at surprising and valuable results. Others won’t, and will decide it’s not for them. Both are valid, your mileage may vary, keep an open mind, and play YOUR way – no one else’s.