is this can affects to seo and accessibility of website if i use or not some w3c xhtml 1.0 strict valid tags like these disputed tags:

[list=]big[/list]
[list=]small[/list]
[list=]br[/list]
[list=]hr[/list]
[list=]b[/list]
[list=]big[/list]
[list=]i[/list]
[list=]noscript[/list]
[list=]tt[/list]

and many more.

these are not unanimously suggested by web experts.