If I run a blog or something in my subdomain like
www.sub.name.net is it going to have any decreasing affect like decrease traffic through search engines or low ranking through on engines?
Subdomains and subdirectories are essentially equal in Google's eyes and probably the other search engines as well. Choose which one is easier for you to maintain and meets possible future growth needs.
No it won't affect your traffic.
But it is always a better option to have your blog as part of your overall domain not as a sub domain or its own domain, as the blog is going to have regular updated content which improves the domain rating and also the blog is more likely to have people link to it. Which again helps improve your domain's authority and will mean the rest of the site ranks higher.
Here is a more in-depth review.
No it won't affect traffic in a negative way on your main domain, but according to this question the vice versa (I mean having your blog in a subdirectory) might greatly affect your traffic on the main website in a positive way.
This topic was dicussed also here and they come to this conclusion:
if you’d like to build the equity of one web site, I suggest using a subfolder.
If you’d like to build an entire new entity with its own equity, launch a subdomain