According to the Alpha + .2 rules:
Strategic Bombing Raids procedure:
• Escorts fire @1, and interceptor casualties are immediately removed.
• Bombers fire @ 1 and interceptors fire @ 2. Remove bomber and interceptor casualties (escorts may be taken as casualties only after all bombers are eliminated).
• Surviving bombers are assigned a specific target (IC, airbase or naval base) if more than one type is in the territory.
• The target fires its AA defenses at the attacking aircraft - @1
• Surviving bombers attack their target, looking for the highest number possible.
The escorts can try to shoot down the interceptors, reducing casualties when the interceptors fire back. So they are useful. The interception rules do make SBRs less useful, though, because there are generally other places you want to use your fighters but nowhere else for the defender to use their fighters.