Apps that are poorly written can have significant effects. Download the Fort Worth Star Telegram app, and the Fox News app. Watch what happens to performance on the OG. Poorly programmed apps can ef up phone performance. If you have Gingerbread you can watch for culprit apps on your phone just by taking a look at running services. If you haven't ran an app, and it just wakes itself up anyway and starts running in the background, there's a good bet that is probably an app you wouldn't want on your phone.
Most of these news websites have crappy apps, but also have mobile versions of webpages that work just as well, and won't stink up the phone. So I just bookmarked the mobile version of the webpages I like then called it a day.
Even though I don't like giving much credit to Moto they are correct in pointing out that crappy apps will have a negative effect on phone performance.