There are a number of good Buddhist discussion forums online, but Reddit is not one of them.
When I was first learning about Buddhism, I stumbled across a few relevant subreddits. I thought it was a good use of my time to browse these subreddits on a regular basis and even contribute to the discussions (or might I say commentary). I was wrong.
The very nature of Reddit does not align with the goals of those seeking to deepen their spirituality. So while it might be useful to glance at when you're first learning about Buddhism, the value drops off quickly.
Let's see why.
People ask the same questions. I remember seeing nearly identical questions week after week, which is unacceptable on a searchable forum where every previous post is still available.
People ask easy questions. Many questions could be answered with a little research, completely eliminating the need for asking such questions in the first place.
It is a content mill. Aside from the questions, it seems like some people post links just to gain a few upvotes. This kind of feedback loop encourages quantity over quality. It motivates people to post content they would have otherwise never posted, which is good for Reddit's business model but bad for those seeking truly valuable material to learn from.
Quotes, pretty pictures, anything short and sweet and easily digestible gets tons of upvotes. This is no surprise because this kind of content appeals to more people, even those who are not Buddhist.
There are a few gems, but you wouldn't waste time panning for a single fleck of gold in a huge river when there is a stream of flowing gold nearby, would you? In the same way, it is better to use your time online in places where you gain the most value.
What would be a good alternative?
I would recommend checking out Dhamma Wheel (Dharma Wheel for Mahayana and Vajrayana) and Dhammaloka.
The pace is slower on these forums. You won't have a feed of content to wake up to, but the discussions are deeper, the people are more interested, and the wisdom you can gain is far greater than anything you might find on Reddit.