Several of my WordPress installs are on hosts using LiteSpeed along with their WordPress Plug-In. Using various website 'speed' and mobility worthyness grading sites the improvements have been VERY significant in relation to DOM Fully Loaded time.
I've seen very little change in Time To first Byte (compared to other caching solutions), which doesn't surprise me being an old server guy but newbs persist in asking if it changed. Most improvement in TTFB are related to backend issues, the Database being a larger component thereof.
The biggest change most will see is the Plugin's combining of CSS Style Sheets and JavaScripts reducing the number HTTP requests, most times by over 25%. Less requests = less time to load all DOM objects under their influence.
Script blocking issues and above the fold rendering aka asynchronous vs synchronous improvements are also a benefit of the server/plugin combo's custom solutions. The developers are VERY responsive to issues encountered in this sub topic with resultant hotfixes being offered in hours (vs week or months with other servers)
Yes, there are other servers types out there that can be performance tweaked to equal and sometimes exceed the server and plugin combo's improvements but they require an A++ level Subject Matter Expert on the alternatives. With LiteSpeed they are the SME that you get on your staff for a fee (a yearly subscription for the server's owner).
