Because you don't cash out your entire bank account and put it in a backpack every time you run to the corner store - and in turn you shouldn't be bringing your cold storage master seed around with you!
Our solution for mobile payments is permissioned signing. Once you pair a device with the Lattice1 you can set up a user specified spending allowance for a given time period - it will generate a remote hardware signature as long as you stay under this limit. Right now you can do this with the GridPlus Web Wallet on your phone or computer to spend ETH and BTC on the go.
1. In your GridPlus We Wallet, select Limits in the menu on the left.
2. You can now enter the spending limit you can spend with a remote hardware signature and the time period after which the limit resets. You can switch between different coins and change the time unit.
3. When you click on Set limit, you will prompted to add this spending limit as a new permission on your Lattice1 screen - press Yes.
4. This creates a permission on your Lattice1. You're done!
If you want to change or remove the limit in the future, you have to remove the permission from your device first - go to Permissions → GridPlus Web Wallet → ETH/BTC → Delete.