Rhythm is one of the main building blocks of creating music, and without a good sense of rhythm, you just can't be a great musician. We've all heard players that had great sounds or amazing technique, but without a good sense of rhythm, it just doesn't fit together. The right notes must be played at the right time.
Metronomes are very useful tools that when used well, will greatly help your sense of rhythm, and today we have some interesting possibilities. When I first started playing the trumpet, you could buy cheap wind-up metronomes, but they just didn't last very long. Electronic metronomes were very expensive at the time.
Today, we have many good electronic metronomes. Some of the best incorporate both a metronome and a tuner in one component. There is even one out now that has a clip-on attachment that gives a physical vibration for the beat. Unfortunately, many metronomes just sit in the instrument case unused. That definitely won't help.
To get the most benefit, you must use it and use it correctly. First, I believe you should combine it with a good foot tap. There are people that believe you shouldn't tap your foot. I'm not one of them. I've seen too many students make considerable improvement by just adding a steady foot tap to their playing.
Next, you need to add a subdivision of the beat if your metronome allows for that. I would only purchase a metronome that has the ability to subdivide into eighth notes, triplets, and sixteenth notes.
The use of a metronome will greatly improve your playing. Do yourself a favor. Get one and use it every time you play. Remember, a right note at the wrong time is a wrong note.