Now firstly what are extra URL parameters?
For most of you,you may have seen a URL that looks like this 'XYZ.com/pagename.php?id=5 etc
These are what are known as dirty URL's, that means if you look at them they would look really messy and disorganized!
Now the answer to the question do extra parameters impact SEO,that could be argued either way.
But i would probably lean more towards,saying probably!
That depends upon the level of competition which the site owner was operating in.So if you were operating in a very low competition space an you are using using dirty URL's with query string parameters you might be able to get away with it to some extent.
However if you are working in an extremely competitive space that it is certainly not best practice.
I would always advise site owners to work towards what i call cling URL's.This means using a sensible URL structure something like XYZ.com/category/subcategory
So basically a clean looking URL which does not have a bunch of query string parameters at the end.
Now there are a few reasons why you should use clean URL's
firstly the are easier for us to understand,we can take a quick look through the search results and get a good idea of what that page is about,based upon not only the title tag in the description but also the URL as well.
In addition to that it makes it easier for the search engines to understand what your page is all about,also and it is probably worth noting that Google bold highlights certain terms within your URL structure that match or relate to the search of which a user enters.
Here are a few more additional tips for an in depth answer.
Firstly always work towards clean URL's this is best practice.
Secondly always implement a sensible URL structure,you really should be working towards using categories,sub categories or a structure that will make sense to you and to your visitors.
Also more importantly implementing a site structure that you can track and manage.
Next of course you should implement keywords where ever you can,now remember that don't get carried away with this because i have seen a lot of people stuffing keywords into their URL parameters and it becomes an absolute 'dog's breakfast!'
So implement keywords within your URL's but don't get carried away with it.
OK next point,be mindful of the length of your URL.URL's or dirty URL's can get really messy but also if your are going to be implementing categories and sub categories make sure that your URL does not become too long.
I see a a lot of web masters implementing a lot of categories and sub categories and end up creating this big long URL which looks absolutely awful. Now of course i should mention eEcommerce sites in particular,because ecommerce sites are renowned for query string parameters within their URL structures this is mostly because of the way which they are built.
People navigate around such sites they might filter by certain results or they will perform a search,where there will be several products differentiated by color or size so you will end up with all this trailing URL parameter.
the best way to overcome this is by setting canonical URL's.These are URL's that you want Google to index and not and of the extra parameters!
Conclusion Ok so that is it for this article thank you for reading i hope this helps you out!