Using a border along the edges of your lawn is generally a good idea. Turf is very aggressive by nature. If you don’t have some kind of solid border between your lawn and your planter beds then your lawn will very likely creep into your beds and become a weed there. Using a border won’t keep all of your lawn out of your planter beds all the time but it will definitely help. And the more solid the border the better it will be at keeping your lawn in lawn areas. Of all the borders I have observed, cement borders are the best at providing a solid wall against encroaching grass. Cement borders are one of the more expensive types of borders but as far as permanence goes, in this case you really do get what you are paying for.
If you are looking for something a little less permanent but stable, a square-cut log that has been well-treated for resistance to the elements does well. You can dig a straight trench where you intend to place it and then tamp the ground firmly around it. This is also a much less expensive option. For a curved area, cut the log to appropriate lengths and angle them as needed. It may require more work on your part, as opposed to hiring an install crew to put cement borders in, but it is less expensive.