Switching from lumia 630 to 620

I think yes. That's something I would definitely do.

(the following are off the top of my head)
Main points for:
higher quality display
more features (NFC, front facing camera (?), flash)

main cons:
much smaller battery
performance might not be as good
 
If you switch to the 630 you are going to have NFC and a camera flash, ambient light sensor, and a higher quality display.

But you are definitely going to have much worse performance, so I would recommend if you stuck to the Lumia 630 instead.

But it depends on your preferences, you could alternately save up for the Lumia 730 or 830.