There are a few things that you need to know when it comes to stretching and working out.
First, there are four different types of stretching.
- Static - The traditional "reach and hold", usually done for 20-40 seconds 2 or 3 times per stretch.
- Dynamic - Active movement, usually done in the manner of what you're about to exercise. Skipping, butt kicks, high knee drills are examples of dynamic streching before a run.
- Ballistic - The bouncing reach. Used to be quite common, then fell out of favor (Stretch reflex can cause injuries/tears), but studies have shown it increases flexibility faster than static.
- PNF - Proprioceptive Neuromuscular Facilitation - This is an advanced stretch done with a partner. Not recommended as a beginner. Uses a stretch, contract against resistance, deeper stretch cycle.
What you are actually doing when you stretch is training your mind what the "safe" limits of your range of motion (ROM) are. A person who is unconscious would have a much wider ROM than when they were awake. The body protects itself against tears by limiting how far a muscle can stretch. By actively pushing past that on a regular basis, you can move your set point.
Now, there have been studies that show static stretching right before a power based activity can reduce the effectiveness and the strength available for the workout, but even that is a little murky and a few studies have shown brief static stretching in between sets may be beneficial [Decent writeup here].
I don't know of any studies that have shown stretching afterwards reduces the gains of the workout, but consider that extreme stretching (i.e. trying to increase flexibility) can also introduce micro tears in the muscle, so you may be delaying recovery.
My personal regimen is to do a light, 10-15 minute routine after weight workouts, and a deeper more intense 30 minute session after plyo/active workouts or on off days (After a warmup, never static stretch cold muscles).
In short, the science is still somewhat mixed on this, but there are more studies than not showing static stretching before a workout reduces available power. So, do an active, dynamic warmup of 5-15 minutes before, and save the static for after. If your body is used to it, then there is no problem with doing deep stretches every day, there are many yoga practitioners that do this. I would respect the need for rest days and schedule one every 3-4 days, however.