Short answer - No
Long answer ---
There are a handful of sweeps which require you to subscribe to emails and free newsletters, but they will say that right on the entry form and/or in the rules. Also, they may say that you must be subscribed during the entry period, but can unsubscribe later.
Most sweeps do not require you to subscribe. It is an option and if you read carefully, you can check (or sometimes uncheck) if you do not wish to subscribe.
It should not strengthen or weaken your chances. The exception is for things like blog sweeps where they say things like, you get 1 extra entry for subscribing, 1 extra entry for referring a friend, tweeting, sharing, etc., etc.....but no, for regular sweeps it should not affect your entry.
One of my very first wins, and still my biggest was a diamond ring. I did not subscribe! I did feel bad after I won, but I doubt that the personnel doing the prize fulfillment were even aware of my status as a nonsubscriber. Since then, I subscribed to lots of things, which is dumb, I never had another big win, and I have tons of daily newsletters...so I am trying not to subscribe anymore.