When I first started sweeping I was just like you...thinking of any easy way to win without filling out the forms with my auto fill program. I spent a lot of time searching the Internet (and I mean a lot) pertaining to the topic. I never did use a automatic sweeping entry service & I am sure glad I didn't consider it very long! Here are some aspects I would consider:
1.) Official rules for the more popular, larger, mainstream sweepstakes with better prizes(I think) usually have very specific wording prohibiting 'automatic' entry.
2.) You could lose track of what you have entered and if you see a good sweepstakes you won't be sure you have entered it or not if you don't keep track.
3.) I read online somewhere can't remember where, that many people never received any confirmations of entering any sweeps at all---if--- they didn't fill out the forms themselves.
4.) Captchas mean your entry might not go through without typing in the correct numbers.
So, I myself would advise against it, but like I said I looked into it on the Internet & decided automatic sweeping would Not be for me. My rationale' - Sure I might win a smaller prize who knows. But who needs a DVD or poster lets say from a random site without specific rules...and risk being disqualified from a really good sweepstakes because you enter one too many times. You would really also need opinions from people who have actually tried the sweeping bots to make a 100% informed decision on the topic.