You could be refused entry to DISNEYLAND with a net ticket:(

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The internet ticket is for "any day".

If the park has excess # of visitors on a given day and you reach there late, they refuse entry - asking you to come on another day or go to their California Adventures park which is close by.

Happened to us on Dec 28th and forced us some change of travel plans. (Visited it on Dec 31st by going early).

Also, the cancellation of net tickets is not easy. Can't do on web or phone call but need to mail & get refund as in the case of "mail-in-rebate"