The biggest myth in RV's today is that everybody "Has" to have a slide. Give me a break. If you have a large family the extra space is probably a no brainer. For two and the pooch hardly necessary if you buy the right floor plan in the first place.
The second biggest myth is that you will not be able to sell any RV without slides which is a bigger joke than myth number one. Lots of folks do not "need" a slide and are smart enough to see the many advantages of not having them.
The reliability of slide on the newer RV's are excellent (older units... not so much), but the bottom line is there are two kinds of folks with slides....
Those that have had trouble and those that will... there is no third category.
For those who would dispute this, and we frequently see comments that slide problems are rare... try reading this Forum, one of the most common topics are the multitude of problems folks encounter with their slides. Now none of them are the end of the world but most are a serious PITA and not cheap to correct.
If you need a slide or more than one by all means go for it. Just be aware that they do add cost, weight , complexity, often leak and are harder to heat and cool. Get whatever you need but buy with your eyes wide open (much like many slides get stuck), Ok, OK, Yes, now I am kidding. :B