From: The Great White North!
Air Intercept is an interesting mission.
Pre-1960's I think intercept should be the primary DCA mission because most of your pure fighter aircraft (not all so you need to understand what you have) were designed specifically for this: fast missile launchers but not a lot of loiter time.
Once the late 3rd and 4th generation fighters started coming out (F-4, Mig-23, Mirage SE etc) they had the ability to loiter in an area for a longer time, had mid air refueling, had their own radars, had the weapons load to hold there own etc, they were able to patrol and dominate an airspace and be much more effective air superiority assets. Patrolling is expensive, a lot of wear and tear on airframes and pilots, so you only do it when needed. NORAD for instance still uses intercept because Russian Bears are not as frequent as they used to be.
I think that a good tactic in a modern fight is a mix of the two missions. A light patrol to act as the 'trip-wire' backed up by several layers of intercept with distance limits from the base. The effect here is a layered defence, throw in a SAM belt and you truly make the attackers job difficult.
Its also important to realize that intercept is almost purely defensive in nature while patrol can and in my opinion should be used offensively.
Like thewood1, I would not use escort for support or SEAD missions. Fighters are too valuable to be tied to this rather passive role. Far better to set A2A patrols that can do more than just this one job, cutting the angles by interceding the Ftrs closer to the threat will be much more efficient and effective.