The main drawback is that, because they are free to enter, there will be a lot of entrants. So, to counteract this, you may have to enter a lot of free competitions before you're eventually successful.
When the prize is not so good, or when the entry process is more complex, competitions will generally receive fewer entries. For example, a competition that requires a tie breaker such as "If I won the prize I would..." will receive fewer entries that one that just requires a name and email address (dependant on the prize).
To increase your chances of winning online competitions it's certainly worth entering the prize draws that are a bit harder to enter, if you have the time, but there's plenty of choice when it comes to competitions whether they are run on the organiser's website, Facebook, Twitter, or somewhere else.
Nick Gandy, manager of http://www.competitionstoday.co.uk, said "In the current climate, with mounting financial pressures, winning a free competition perhaps gives even more pleasure that it has done in the past."
If you are going to enter free competitions, one thing you should certainly consider is to set up a dedicated email address for this purpose with hotmail.com, gmail.com, etc. That way, any potential spam type email can be minimised and you can continue to keep your personal and business email addresses free of any extra clutter that may result from you entering lots of online competitions.
There's a lot of fantastic prizes out there to be won including holidays, flights, iPads, TVs, shopping sprees, sports tickets, cash, and much more. The possibilities are endless, but you will need to have some luck on your side.