Postage on certain items is cheaper via meter than stamps. Example, first class (<1.0 oz) is 58 cents with a stamp, 53 cents via the postage meter. Ditto for 2.0 ounce mail (78 cents via stamp vs 73 cents with meter).
I personally really love the convenience of having the meter. We can download money to the meter online.
However, be careful about certified mail via only the meter (or only stamps.com) without getting the USPS postmark on the receipt, which PROVES when the USPS receives the item. There can be question for the timely-mailed, timely-filed rule when using stamps.com and the like without getting the actual postmark from the USPS.