The flexibility is an advantage because you can come to the course when you have the time, energy and initiative to learn.

It can be a disadvantage if you don't find the self-discipline to structure your time, energy and initiative.

Condensed summer schedules can increase that disadvantage. Students in summer session courses spend 90 minutes in the classroom each day and at least that much time in preparation each day. You should expect to spend a similar amount of time online.  

You will be judged on the quantity and quality of your participation.  It probably will be best to find quickly a routine and structure that allows you to learn online.

If you do not have a personal computer online, Lehigh's computer labs have generous summer schedules and no crowds.