It is free, however there are certainly some disadvantages of freerolls:
One of the main disadvantages of a freeroll poker tournament is that they are very time consuming. This means sitting in front of your computer for up to 2-3 hours and in the end you might end up with nothing. In case you are going to play at a $1,000 you will see around 500 players competing against each other and only 50 of them are going to take something home.

If you are going to compare a freeroll tournament to a normal buy in tournament, the winnings at a freeroll tournament are going to be lower and in case you have already managed gain some skills to play at an online poker tournament you should go for the paid ones since the winnings are consistently higher.
Many online poker rooms out there offer freeroll tournaments. In case you are after freerolls, you just have to visit the promotions section on the most popular online poker rooms and you will get the chance to find plenty of information available about the tournaments offered.

However before joining make sure that you read exactly what are the terms and conditions of joining that freeroll. This way you will be leaving out all the misinformation that you might have about that freeroll. Also, make sure you can receive a deposit bonus and rakeback at the online poker room you join. For example, you can receive carbon poker rakeback, deposit bonus, and 14 days entry into the daily first time depositors $500 Freeroll.

In the long run however these negatives are far outweighed by the long term difference made by saving money during the time you would normally be getting schooled at the tables.