Had the same issue. It def will caause lag and raise usage. I argued with them for mnths about it because at the time i was over the cap every month. Problem was it was just me using it for video games. Long story short my neighbor was. Using his girlfriends password to downlload movies and stream netflix. Once i figured out show to shutoff the hotspot i usage dropped and speed increased. Needlless to say i droppped comcast for another cable provider and havent had any issue since.
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