This is a very unusual suggestion - I've never once seen any of the SEO experts even hint at something like this. It sounds like something that used to work years ago - a bit like keyword stuffing - and could be considered to be a "black hat" these days.

It certainly doesn't meet Google's (admittedly vague) guidelines - they say you should write content and mark it up for the user, not the search engines. It also doesn't meet any of the standard conventions for writing web pages.

As for negative impact:

• If Google decides this is black hat, they will penalise the ranking.
• If they don't consider it black hat, they still might consider the page over-optimised for that term (depending on the rest of the optimisation), and penalise it
• Even if they don't penalise it, it means the page is optimised for that phrase only and not for for local or long tail searches.
• Google is putting on a lot more emphasis on LSI these days, so repetition of the same keywords is not particularly effective.

As I said, I've never seen this technique even suggested, never mind recommended. Based on all that, I personally wouldn't use it when optimising a site, but then I am clearly more cautious than your client :)

This is a very unusual suggestion - I've never once seen any of the SEO experts even hint at something like this. It sounds like something that used to work years ago - a bit like keyword stuffing - and could be considered to be a "black hat" these days.

It certainly doesn't meet Google's (admittedly vague) guidelines - they say you should write content and mark it up for the user, not the search engines. It also doesn't meet any of the standard conventions for writing web pages.

As for negative impact:

• If Google decides this is black hat, they will penalise the ranking.
• If they don't consider it black hat, they still might consider the page over-optimised for that term (depending on the rest of the optimisation), and penalise it
• Even if they don't penalise it, it means the page is optimised for that phrase only and not for for local or long tail searches.
• Google is putting on a lot more emphasis on LSI these days, so repetition of the same keywords is not particularly effective.

As I said, I've never seen this technique even suggested, never mind recommended. Based on all that, I personally wouldn't use it when optimising a site, but then I am clearly more cautious than your client :)

Update 2022: With Google's Helpful Content Update, they are actively discouraging content written specifically for search engines. While this update applies mainly to the content topic rather than format, I think it's safe to say that using any measure solely to try influence your ranking is discouraged - at best it won't give any SEO benefit at the expense of accessibility.

Moving my answer from Stack Overflow where your question was off-topic

This is a very unusual suggestion - I've never once seen any of the SEO experts even hint at something like this. It sounds like something that used to work years ago - a bit like keyword stuffing - and could be considered to be a "black hat" these days.

It certainly doesn't meet Google's (admittedly vague) guidelines - they say you should write content and mark it up for the user, not the search engines. It also doesn't meet any of the standard conventions for writing web pages.

As for negative impact:

• If Google decides this is black hat, they will penalise the ranking.
• If they don't consider it black hat, they still might consider the page over-optimised for that term (depending on the rest of the optimisation), and penalise it
• Even if they don't penalise it, it means the page is optimised for that phrase only and not for for local or long tail searches.
• Google is putting on a lot more emphasis on LSI these days, so repetition of the same keywords is not particularly effective.

As I said, I've never seen this technique even suggested, never mind recommended. Based on all that, I personally wouldn't use it when optimising a site, but then I am clearly more cautious than your client :)

This is a very unusual suggestion - I've never once seen any of the SEO experts even hint at something like this. It sounds like something that used to work years ago - a bit like keyword stuffing - and could be considered to be a "black hat" these days.

It certainly doesn't meet Google's (admittedly vague) guidelines - they say you should write content and mark it up for the user, not the search engines. It also doesn't meet any of the standard conventions for writing web pages.

As for negative impact:

• If Google decides this is black hat, they will penalise the ranking.
• If they don't consider it black hat, they still might consider the page over-optimised for that term (depending on the rest of the optimisation), and penalise it
• Even if they don't penalise it, it means the page is optimised for that phrase only and not for for local or long tail searches.
• Google is putting on a lot more emphasis on LSI these days, so repetition of the same keywords is not particularly effective.

As I said, I've never seen this technique even suggested, never mind recommended. Based on all that, I personally wouldn't use it when optimising a site, but then I am clearly more cautious than your client :)