Respringing the "right way" allows SpringBoard to save usage data. Otherwise, your usage data is lost and the standby/usage times are reset to "–" until you fully charge again.
Tweaks that respring the right way
(There are probably a few more)
How to respring the right way
[(SpringBoard *)[UIApplication sharedApplication] _relaunchSpringBoardNow];
From the command line:
Install cycript (Cydia will need to be in developer mode to find it). Create /usr/bin/spring and enter the following contents:
#!/usr/bin/cycript -p SpringBoard [[SpringBoard sharedApplication] _relaunchSpringBoardNow];
chmod +x /usr/bin/spring to make it executable, and now you can run
spring to respring. (You could also call it
respring if /usr/bin/respring doesn't already exist.)
Can there be a "fix" for tweaks that don't respring the right way?
I'm working on it, not a high priority to get it done though.