By default in WordPress 1.5 and onwards, a post's sanitised name that appears in a permalink structure is checked for duplication and a numeral is app
A post titled "A Witty Quote" for example, has a post slug (which is used in a post's permalink) of 'a-witty-quote'. A second post titled "A wiTTy QUoTe" (or something similar) would have a post slug of 'a-witty-quote-2'. If you want the second post slug to be 'a-witty-quote' instead of 'a-witty-quote-2', use this plugin.
If you're asking, it probably isn't! To be useful, the following should all be true:
No. Singular merely repeats WordPress' own method of creating a post slug. That is, it takes the title of the post and sanitises it. All Singular does is skip the code that checks for a duplicate that could possibly add a numeral suffix.
If you have a unique permalink structure similar to that described above, no. However, the numeral is put there for a reason. If you store archives by category, for example, and two posts in the same category have a similar title, both posts will resolve to the same permalink. Which one will take priority is up to your .htaccess file. Ensure you understand the implications of fiddling with your permalink structure before you run with this. That said, it won't actually delete any posts, it just might make them hard to find...