When your message and timing is relevant, any channel will work. LinkedIn is no exception, it always works better when you are already connected and your contact has some idea of what you do and how expert you are (c.f. @byalexai relevant post below). I have done it in the past.

I think a lot of factors matter: the level of your personal account, your message, your product. So for some it will work great, but for others it won't.

I always ask myself, would I reply to this? If the answer’s yes, I send it.

If you have the authority - yes If you don't have the authority - no Focus on building your brand

If you do it properly and authentically it works.

Not really but sometimes Yes.

Its not easy but if you are consistent, you may land on job or get connected with clients.