The single biggest benefit of design patterns in my opinion is that it gives developers a common vocabulary to talk about software solutions.
If I say, "We should implement this using the singleton pattern", we have a common point of reference to begin discussing whether or not that is a good idea without me having to actually implement the solution first so you know what I mean.
Add in readability and maintainability that comes with familiar solutions to common problems, instead of every developer trying to solve the problem in their own way over an over again.
Pretty important. Software can be made without them, but it's certainly a lot harder.
