will it cost me more usage while on wifi than LAN?

[Rvignesh]

i'm using airtel broadband unlimited plan. 2mbps speed and 20gb FUP (fair usage policy). Over 20gb my speed will b reduced to 256kbps. i hav 3 devices viz laptop, phone and tab for internet connection... phone and tab through wifi and laptop thru wired LAN. i use laptop for huge downloads and phone&tab jus fr browsing... My modem is not centerized for accessing wifi all over my home.... but if i get centerized i'll loose that wired connection fr my laptop (in which i'm doing huge downloads and 75% of whole browsing). My question is Can i go wirelessly even with my lap? some are saying LAN is preferrable. why so?? if i go wirelessly will i get affected by any wastages.... some are sayng that you may get wastage upto 0.5 gb in that overall 20gb. And also lemme know about the consistency in speed(considering full signal strength with no hindrance) will it be less when compared that of wired?

thanks for reading my long question and would be more thankful if answered... HAPPY NEW YEAR TO ALL