Seo4SMF Url's ...

Are 2 good reasons to do that:
1. If you have a big forum and if you keep all the pretty url's in database (is the single possibility to remove id's from topics and boards) than will be nasty because for each url you will have a query on db and a forum page can have more than 100 links. Think .... you have 40 users in the same time and on each page you have 20 links ... just do simple calculation to see how increase the database query / memory in this case.

2. Duplicate topic title ... if you have duplicate titles you need to have something to distinct them and in this case you will need to add an ID anyway.

Anyway any search engine will not made any difference between one url with topic id in it and one without id.

Regards