Removing PCR duplicates in RNA-seq Analysis
For normal RNA-seq PCR duplicates are normally kept in, but the duplication rate can be used as a quality control: The higher the duplication rate, the lower the quality. For expression analysis, it is probably best to discard high duplication rate samples, rather than deduplicate them. 

In general, the smaller the amount of RNA input into the library prepartion the worst the duplication. Many protocols for very low input quantities (such as single cell) include random barcodes called UMIs (Unique Molecular Identifiers). These allow PCR duplicates to be distinguished from genuinely independent molecules that just happen to have the sample mapping position.