I don't think it would be useful for items you mentioned, but you could probably set up a linked team with them to end up with a 2gbit link, which would also make the connection redundant in the case that a cable went bad or something like that. Depending on the cards and the software that comes with them you may need a switch that also supported the 803.3ad standard, but most likely it will let you team them without requiring a switch that supports it as most home routers/switches do not unless running custom firmware.
It would not speed up your internet connection.
It would not decrease latency
It would allow for a 2gbit connection to your machine on the internal network if you had other devices streaming from it etc.
It also useful if you are using the machine itself as a router/firewall etc, but that does not sound like what you have intended for it.