If you are 4 before a meal, then nothing wrong with that, I would myself air of caution when it came to injecting for a meal though, as if you are eating a slow adsorbing carb/high fat content meal the insulin could send you hypo before the carbs kicked I would be more likely to inject my dose either 1/2 way through the meal or just after I finished...
If you drive then a 4 would mean you would need a snack, to ensure that you didn't hypo at the wheel..
I wouldn't go to bed on a 4, as you would likely have a hypo through the night
I wouldn't exercise on a 4 either
IF my meal was going to be a while, then I would have a snack to ensure that I didn't fall below before my meal...
The problem with running your BG's near the 4 mark too much can cause you to become hypo unaware, which can cause all sorts of problems, such as ending up in A&E or even intensive care, and again if you drive hypo unawareness effects your driving licence it will be taken off you as it's aginst the law to hold a driving licence let alone drive when you have hypo unwareness..