Encoder Decoder Sequences: How Long is Too Long?

In machine learning many times we deal with the input being a sequence and the output also a sequence. We call such a problem a sequence-to-sequence problem. A popular architecture for dealing with the sequence-to-sequence problem is the encoder decoder architecture. The encoder converts the variable length input sequence to a fixed length context vector, and the decoder converts the fixed length context vector to a variable length output sequence. I have been reading enough literature (for an example, take a look at this article) that says the disadvantage of the encoder decoder architecture is that irrespective of the length…...