We chose to get a trailer without slides. We were buying used (about 10 years) and mostly do boondocking (sometimes down miles of dirt).
We are planning to keep the trailer for a long time and wanted to limit the potential failures. We made the decision that the extra space wasn't worth the added complexity for our planned use.
Everyone has to make up their own mind based on their ownership and usage patterns. If we only camped at campgrounds on pavement and traded up every few years then it would be a different story.