GA is riskier, but can be administered much faster than a spinal block, hence why they use GA for emergency sections where the baby is distressed and they need to get it out ASAP. Generally they prefer not to use GA for planned or less urgent unplanned sections (such as for example if you turn up to the hospital in labour and they find baby is breech or baby's head is in a bad position and won't come out naturally but isn't in any distress).
With GA you also miss out on immediate skin to skin. how long you're kept under will depend on the circumstances, but it does take a while to sew everything back up after they get the baby out (can't remember exactly, but think it was something along the lines of they can get the baby out in about 5min with a GA, but it then takes an hour or two to sew all the layers back up). With the local, you can be holding baby and having skin to skin etc while they sew you up.