If every dark cloud has a silver lining, then perhaps the converse is true when it comes to human endeavors, especially in a time of war.

Take the case of using unmanned aerial vehicles -- so-called drones -- in decimating the leadership and lower-echelon ranks of al-Qaida in Afghanistan and in the lawless tribal areas of neighboring Pakistan, where they maintain headquarters, training and supply areas.

It's estimated the United States has conducted at least 50 airstrikes using drones this year. Among the dead: Atiyah Abd al-Rahman, al-Qaida's second in command in Southwest Asia, who was killed in Pakistan in August. And more are likely destined to fall by the wayside as Washington continues to ramp up attacks with the silent killers.

"Now is the moment, following what happened to (Osama) bin Laden, to put maximum pressure," on al-Qaida, said Leon Panetta, former CIA director.

But some are concerned over the long-term ramifications of drone strikes for the United States and America's allies in terms of intelligence lost by killing rather than capturing terrorist leaders.

"In the beginning of the war on terrorism we weren't killing al-Qaida leaders we were capturing them, developing tremendous intelligence from them about high-value targets but also about how al-Qaida functions, it's strategy," said counter-terrorism expert and Georgetown University Professor Bruce Hoffman.

"It's true we're being deprived of that intelligence now but of course the end product of both efforts is to prevent attacks on the United States."

But "you can't quibble with it too much because we have been successful," he said.

In the 10 years since al-Qaida attacked the United States hundreds of terrorism suspects have been detained, sent to clandestine third-countries facilities for interrogation by CIA officers about leadership, strategies, members and sympathizers.

It is believed that just one slip by a suspect held at Guantanamo Bay, Cuba, helped set in motion an intelligence-gathering effort that years later to bin Laden's courier being found and tracked, leading to the terror leader's demise at the hands of U.S. troops last May.

How many terror cells were disrupted and attacks thwarted may never been known but intelligence professionals say interrogation of suspects is essential.

Renditions are now banned, the administration of U.S. President Barak Obama has apparently barred Guantanamo Bay from accepting new prisoners and is relying on third countries.

U.S. Navy Adm. William McRaven, commander of U.S. Special Operations Command, said terrorist suspects captured in countries other than Afghanistan or Iraq are taken aboard U.S. ships, questioned and then either sent to the United States for trial in civilian courts, handed over to third countries or let go.

Questioning is done by rules stipulated in the U.S. Army Field Manual -- said to be more restrictive than practices U.S. police forces follow.

Former CIA operations officer Charles Faddis, who is opposed to "enhanced" interrogation techniques such as water boarding, said he believes the administration's emphasis on drone strikes may have a political element in it: avoidance of issues such as civilian trials and their restrictive rules on evidence allowed and alleged human rights violations of suspects.

"It's rather ironic that because of concerns over human rights, that we are so worried about human rights by holding and questioning them, that we have now adopted a policy where we won't capture you, we'll just kill you," Faddis said.

Al-Qaida is an amorphous organization with offshoots around the world that have all proved adept at changing strategies and tactics as the United States and its allies do the same.

The question now is: Could an increased emphasis on drone strikes lead to a paucity of intelligence material that is vital in meeting the challenges in the war on terrorism proactively?