Sure, it renders slower. I've just signed my 25th professional client, and I have never yet had a client who even mentioned rendering speed, let alone was willing to make any trade-off for it.
That's because understanding rendering speed is your job, not the client's job. What the client will be saying is things like "Why are my conversions so low?", "My site doesn't appear in search results." and "My friend's neighbour's dog-sitter told me my website sucks because it takes ages to load." It's your job to translate those comments in to meaningful actions, like optimizing rendering speed.
I guess so. Fortunately, none of my clients are in those kinds of businesses.
Which is sort of a weird point. So much of the web development blogosphere assumes that the reader is working on a site that sells some product direct to the public, who are very fickle, and will abandon your site quickly. Undoubtedly that industry does exist, but I've just never been anywhere near it.
That's because understanding rendering speed is your job, not the client's job. What the client will be saying is things like "Why are my conversions so low?", "My site doesn't appear in search results." and "My friend's neighbour's dog-sitter told me my website sucks because it takes ages to load." It's your job to translate those comments in to meaningful actions, like optimizing rendering speed.