can they slow down my laptop - generally no.
Are they very important can they safe guard? - yes.
Do you download them? - Yes always.
Do they take a very long time? - if you're on dial-up they can. On BB, they're usually pretty fas.
Are they safe to download them? - yes. Safety is not an issue. The whole point of many of them is to increase the safety and security of your internet 'experience'
Whats the best way to download them when your on the net or doing some important work on the computer. - It's up to you. If you have a fast laptop, you can let them download in the background whilst you're doing other things. If your laptop/connection is slow let them download whilst you go off and have a cup of tea.