If you have the time and means, it can be very helpful to read other systems than what you are running. Even if your group is a dedicated one system group - as many groups can be - there is still value in reading other systems. Today I want to talk about a couple benefits you can find, and why it may be worth your time.
GM Advice Is Often Universal
Almost every game system gives advice for how to run the game. The thing is, while system mechanics are different from game to game, the advice to run games is often universal. Different GMs and writers have different takes on what makes a good session, and each game can have different focuses on tone. L5R is all about Honor vs. Dishonor and Law vs. Chaos, while D&D tends to be more about Good vs. Evil (but also has that Law/Chaos dynamic.) Themes that work in L5R can work in D&D. Even better, they can help your D&D game have a more unique flavor by hitting notes that maybe aren't always
Different Mechanics For The Same Problems
One of the key jobs a GM has in any session is making rulings for how to resolve things that either don't have explicit rules for them in the system, or where those rules may not be known at the time and you don't have the time or inclination to go digging through a rulebook.
By reading different systems you expose yourself to different approaches to these problems. Fantasy Age may not have rules for how to do an acrobatic trick into an attack, but Exalted or 7th Sea might. Obviously those mechanics aren't going to port over directly, but you still get an impression as to how it might work, and that gets you closer than you were before.
Other systems have simple mechanics that just work for certain things. The Advantage/Disadvantage rule from D&D 5e can work in any D20 based game as a quick way to show a beneficial or harmful scenario for the players. The raise mechanic from Roll & Keep where a player can call their own critical by getting extra effect over a base success by raising a TN is also easy enough to port over. But if you're not familiar with how those systems work, they're not tools in your tool box.
You Might Find Inspiration You Like
Finally, by breaking out of the familiar system you expose yourself to outside ideas, and that is good fuel for your own ideas and thoughts. Just seeing things you won't see in your familiar system can spawn all sorts of interesting ideas.
A friend of mine sent his D&D game to Rokugan where they are dealing with the Shadowlands, the Taint, and enemies and allies that just don't think like they do. It's bringing all sorts of interesting dynamics to their game, especially for the players unfamiliar with Rokugan and how it works. This isn't an experience they could have if the GM wasn't an L5R fan and a D&D fan at the same time.
This isn't limited to gaming books either. You running a fantasy? See what ideas you can steal from Sci-Fi. After all, any sufficiently advanced tech is indistinguishable from magic, right? Bring in aspects from a super hero game, or bring some fantasy elements into your cyberpunk game (that is how you get Shadowrun, so be careful ;))
Make it weird. Make it fun.