It would take a highly sensitive palette to discern between fresh or bottled lemon juice. However, some use fresh for many reasons. First, to stay as authentic as possible. Second, some bottled lemon juice contains preservatives. Third, it is just as easy to juice a lemon then pour it from the bottle.
Fresh lemons will keep for up to two weeks in the 'fridge. Buy them by the half dozen, and if you don't use them, you can always make a centerpiece for your table. No desire for the centerpiece? Try making fresh lemonade, and you will see where the difference between fresh and concentrate lemon juice comes from.
Lemon zest is an undervalued resource. Lemon zest is great in desserts and is even better with fresh vegetables! When steaming veggies, simply add a tablespoon of lemon zest to your water. You will have a hint of lemon in the taste of whatever vegetable you are cooking. Try with fresh green beans and asparagus!