It seems the answer depends on which Pi you are using and which header is on it.
If you have the old 26 pin header, you only have SPI0 available. It doesn't look like anything interesting is muxed with SPI0, so the only downside would be that you permanently take up a couple of GPIOs if you permanently enable SPI0.
If you have the new 40 pin header, you still have SPI0 available with the same properties. Additionally, you also have SPI1 (one of the AUX SPI) available, so if you include this in your "always activate SPI" then you might want to know that there is more functionality shared on these pins. It looks like there are a couple of GP clocks, 2 PWM pins and a BSC slave interface. And of course, they are GPIO pins too.