Sewn Bindings also have the advantage that they can take many more pages than Channel Bindings, usually up to 400-500 pages in a single binding (assuming 80gsm paper).
Pitfalls:
Unfortunately the cheapest sewn bindings tend to have very simple cloth and card covers compared to the textured and plasticised covers of the high street machines. Another thing to watch for is that a simple sewn binding may have covers no bigger than the pages, which can lead to the corners of the book being damaged.
Cost
Surprisingly for many Sewn Bindings are often cheaper than Channel Binding, because they are not done by High Street stores. £5.50 to £6.50 seems to be an average price for cloth covers, going up to £7.00 for very thick card covers.