In my experience/opinion (I don't have a reference at hand) qPCR and RNA-Seq correlate very well, meaning that confirming gene expression from RNA-Seq with qPCR on the same RNA sample is probably unnecessary (by the way, is there any evidence that qPCR is better than RNA-Seq?)
However, since RNA-Seq experiments are often done on small sample sizes (2-4), it makes sense to apply qPCR on many more samples to refine the findings from RNA-Seq, for one or few genes of interest, obviously.
RT-qPCR is often used to confirm experiments, but may not be necessary.
The main difference are that RNASeq is massively parallel but has difficulties with low coverage genes (you lose your statistical power). RT-qPCR will be much more precise for these weakly expressed genes.
Also, you design your primers with RT-qPCR which means it might be easier to study isoforms (just be sure your primers don't overlap, or there will be some competition effects).