Sonars send out pulses of ultrasound to locate objects. Sound travels in waves, not straight lines, and these waves expand in cones, getting wider and wider.
Most sonars can control the range of the sound wave cone by changing the scanning beam frequency. This is important because in different fishing situations different scanning beams will be more or less effective.
Wide beam scanning (Deeper PRO/PRO+ 55° angle; Deeper CHIRP 47° angle) is good for quickly scanning large areas and getting overall information on fish, depth and bottom structure, but the accuracy and detail will be lower. Wide beams are also great for quickly locating fishes. Wide beam scanning is best suited for shallower waters because the cone covers a wider area, the deeper it scans. This means if you are scanning at a depth of 45ft / 13,7 m you will see objects in an area that has a 47ft / 14,3 m diameter.
Narrow beam scanning (Deeper PRO/PRO+ 15° angle; Deeper CHIRP 7° and 16° angle) gives a more precise picture of the bottom structure, fishes and their size, but covers a smaller area. It is better for finding the exact location of fish, as well as the information about the bottom (structure, bottom thickness, vegetation). Narrow beam scanning is also better suited for deeper water, as the cone does not spread as wide.
Recommendation: When using Narrow beams in deep waters, it is important that the Deeper sonar ball is stable in the water, and does not rock around. If the sonar itself is not stable, the quality of the sonar image will be affected.
If the waves are rough, it is better to use a Wide beam.
You can learn more about how sonars and different beams here.