Spoken English Written English
lexical : 20% 30-40%
grammatical : 80% 60%-70%

advantages of reading presentation
giving more information / more details
less mistakes
organize the structure better
less stressful / more comfortable
saving time for being accustomed to presentation(after making a presentation)

disadvantages of reading presentation
less catch the audience feedback / not flexible
it looks to be less prepared and to be less confident / may seem nervous/unprepared
easy to be boring / it could be very boring(impersonal)