Many 5V LED strips can also be operated without a level shifter, especially if the wire between the controller and the LED strip is very short. Sometimes, however, flickering can occur, e.g. the LEDs briefly flash white. Larger disruptions are also possible. With 12V or 24V LED strips, you usually cannot proceed without a level shifter. However, a level shifter is also expressly recommended for 5V LED strips, especially in productive use, to ensure trouble-free operation: a level shifter adapts the signal level of the microcontroller (3.3V) to the signal level of the LED strip (5V for all addressable LED types).
Professional WLED controllers always have an integrated level shifter.