in my opinion I did not know about this before, but now i am quite clear ... it is similar to having a web host where instead of having your database of webpages stored, you keep EA running on your account. So no need to keep your computer running for day and night, well it will sure be a good idea if it does not cost very high. i had some idea about this , this post cleared my other doubts too. Small traders in the beginning of there career can not afford the use of such service. so it is better to think about this once we get enough money and good EA.