Telescope magnification is not nearly as straight forward an issue as most people tend to presume. Common to popular belief, telescopes do not have an inherent magnification. Instead, they will have various magnifications based on what eyepiece is being used.
Two numbers will come into play to determine the magnification. The first is the focal length of the primary lens or mirror which is given the symbol fo ("f" for focal length and "o" for objective which is another name for the main lens or mirror). For my telescope, this is 2,000 millimeters (mm). The second number is the focal length of the eyepiece, fe. The ratio of these (fo/fe) gives the magnification.
I have a small collection of eyepieces that range from 40mm to 5mm. This translates to magnification ranging from 50 to 400! So why don't I always pop in that 5mm eyepiece and get the biggest picture available?
There's lots of different reasons. One is that the higher the magnification, the smaller the area of sky you're looking at, known as the field of view. This creates several problems. To understand them, consider the following. I'm observing the moon using an eyepiece that allows the moon to nearly fill the entire field of view (which it very nearly does with my 32mm eyepiece). The moon is 1/2 of a degree in diameter, so we'll pretend that's the field of view in question. Now, let's say there's a truck rumbling by or a slight breeze, either of which cause the telescope to jiggle a tiny bit, let's say 1/100th of a degree. That's probably greatly exaggerating the real amount of jitter, but bear with me.
For a field of view that's 1/2° wide, that jitter would be causing the image to bounce back and forth 2% of the width of the field. This would be quite annoying. But now let's consider that 5mm eyepiece again. It's zoomed in way more so it would only have a field of view of 0.08°. The same jitter of 0.01° would now be 13% of the width of the field of view! It would be impossible to see anything with it bouncing around that much!
As noted, this is an exaggeration, but the point I'm getting at here is that when you magnify an object more, you also magnify any jitters and jiggles in your telescope which makes things harder to observe.
But there's another consequence of the small field of view. As you know, the Earth is turning. Since we're anchored to it (thanks to gravity), we don't feel that motion and instead, it seems like the sky is turning. This would mean that if I wanted to watch an object continuously, I'd have to make my telescope constantly track that motion. My telescope has a motor that turns the telescope at the exact rate the sky turns, but alas, I lost the power cord for it years ago and even if I still had it, I generally don't have a power outlet in the middle of fields. In other words, my telescope stays still while the sky turns.
Through the eyepiece, this means that the stars will move across the field of view and eventually out the other side, traveling at a consistent angular speed. The result is that they will drift out of eyepieces with high magnification (small field of view) far faster than they will ones with low magnification (large field of view). This is the exact same as how it will take me less time to drive one block (small field of view) than it will one mile (large field of view). Thus, if I want to toss on the high magnification, I'm going to be constantly twiddling my adjustment knobs to keep things centered. Not a huge issue if I'm the only one observing, but when I'm hosting star parties and have 40 people in line wanting to look, constantly butting in to fine tune isn't appreciated!
And that's not the end of the problems with high magnification! A given telescope will have a certain ability to gather light. Simply put, the bigger your main mirror (or lens) the more light you'll collect. The question is what you're going to do with it. With a low magnification, you're not spreading it out too much. But with a high magnification, you're smearing it out "like butter scraped over too much bread" as Bilbo put it in The Fellowship of the Ring. The effect of this is that the object looks fainter. For bright stars this isn't an issue. But quite often, what we want to observe is already quite faint. Making them any dimmer may push it to the very threshold of what the eye can detect for light and the exquisite detail is lost. This is especially true for nebulae.
This has been a rather long answer. When people ask what my magnification is, I generally respond with, "Using this eyepeice, it's (insert magnification here)" and leave it at that for the sake of time. Often they seem somewhat underwhelmed that it's so low. If you were one of those I disappointed, now you know why.