Advantages of Online Tutoring
Students can send papers any time of the day, from anywhere.
Some students learn better in an anonymous setting, without the distractions of the physical presence of a tutor.
Tutors have more time to think over their response.
Students can print the tutor's remarks and study them as often as needed.
Students can learn from the tutor's remarks in a setting of their choice.
Students get experience reading comments about their writing in writing.
Disadvantages of Online Tutoring
The immediacy of one-to-one tutoring is gone.
Tutors have a lot of guess work to do if student don't clearly explain what kind of feedback they'd like from the tutor.
Students might have problems separating the tutor's remarks from their paper and/or applying the tutor's suggestions when they revise.
Some errors might be difficult to handle in an online session.
On the whole, online tutoring is better for global issues, such as essay structure and essay development, while one-to-one tutoring might still be better for teaching grammar.