There are risks, you need to remain online to catch your counter-party cheating. There are ways to outsource this to so-called watchtowers. This can generally be done privately, and the watchtowers generally get to take at least some of the cheater's money.

I haven't heard of any successful malicious channel theft. I have read quite a few stories of people losing local data making it much harder to recover the money in the channel.

As far as I know you have to be on the internet at least once in 30 days, so it's good only for hot wallets. Also for payments over $1k probably right now Bitcoin transaction is more practical (I have heard of $100k lightning transactions though).