Sidechains are about more than simply allowing extra capacity on the bitcoin network. They fundamentally enable the pace of innovation to increase in the cryptocurrency space.
In the past, if someone wanted to improve bitcoin technically (for a trivial example, let's say improving block confirmation times), they had to fork bitcoin, and release an "altcoin" (thus creating an entirely separate currency at the same time). This inevitably led to many bystanders speculating on the altcoins - getting distracted from the technical improvements, and focusing on whether it was a good investment or not. In the past, it was not possible to separate the bitcoin network from the currency.
Sidechains allow us to create entire new blockchain networks, which use the bitcoin currency natively. This means that I can now test changes to the bitcoin protocol, and allow people to move their existing bitcoin (currency) on and off my new network. For a popular sidechain, hosted wallets could even transparently support sending and receiving coins on both networks. This is a major step forward for cryptocurrency, because it means we no longer need every innovation to have 100% consensus on the main bitcoin blockchain - we can simply try out new ideas on sidechains.
Longer term, I can see sidechains allowing us to even migrate to a Bitcoin 2.0 protocol (think IPv6) - once a new standard is formalized, people can begin using the new network in parallel, and eventually everyone will migrate to the new "main" network.
In the past, if someone wanted to improve bitcoin technically (for a trivial example, let's say improving block confirmation times), they had to fork bitcoin, and release an "altcoin" (thus creating an entirely separate currency at the same time). This inevitably led to many bystanders speculating on the altcoins - getting distracted from the technical improvements, and focusing on whether it was a good investment or not. In the past, it was not possible to separate the bitcoin network from the currency.
Sidechains allow us to create entire new blockchain networks, which use the bitcoin currency natively. This means that I can now test changes to the bitcoin protocol, and allow people to move their existing bitcoin (currency) on and off my new network. For a popular sidechain, hosted wallets could even transparently support sending and receiving coins on both networks. This is a major step forward for cryptocurrency, because it means we no longer need every innovation to have 100% consensus on the main bitcoin blockchain - we can simply try out new ideas on sidechains.
Longer term, I can see sidechains allowing us to even migrate to a Bitcoin 2.0 protocol (think IPv6) - once a new standard is formalized, people can begin using the new network in parallel, and eventually everyone will migrate to the new "main" network.