Same anon here, decided to write more on the subject. 1st paragraph is more less repeat. Apologies
Role of Drones:
During the Southern African liberations Wars in the Congo, northern Angola, and Southern Rhodesia, the ‘bush’ in these countries was used to its full advantage by for black terrorists whom conducted their guerrilla operations from it. The foliage concealed their movement through it, and was used a place of refuge from which launch ambushes and hit and run attacks from. Without the overhead vegetation, combatants become extremely exposed to areal observation. Because South Africa has plains and grasslands not bush; Drones can cost effectively take advantage of this. Such as in Yemen, dispute not having an air force, Iran and by extension the Houthis guerrilla [have] found it can achieve ISR – intelligence, surveillance and reconnaissance – by flying drones over the battlefield.”  This can be for both tactical and operational applications. Drones could be very useful to spotting hostile mobs, combatants and potential ambushes along evacuation routes on the battlefield. And for the headquarters they can be used in intelligence gathering as well to see enemy troop movements, concentrations, training camps and build ups.
Drones, even without weaponry, have a vital role bombarding targets as “they [UAVs] are also becoming effective at using drones to call in highly accurate artillery and mortar fire.”  This devolvement of areal recon is not new, over fifty years ago, the marine corps concluded that a “commanders required a realtime information, reconnaissance, security, aerial observation, and target acquisition/designation system that could operate day and night in all kinds of weather. Based upon those needs, obtaining the Advanced Scout Helicopter was mandatory.”  While the project was later scraped due to bureaucratic red tape, it is worth noting that drones fill role of artillery spotters just well and for a much cheaper cost.
Drones can also have an attacking ability. There are two methods of doing so engage targets with onboard weapons like gunship or the expendable option of being a loitering munition or otherwise called suicide drone.
>Technological advancement has given the edges to drones
UVAs are also smaller minimizing their radar profile compared to conventional aircraft.0 the non-metal, foam (?) and carbon fiber drones have low radar signatures and are virtually indivisible to non-interlinked antiquated air defense systems. 0. Both Yemen and the Karabakh War show, Cheap drones against second rate air defense systems are the winning factor. Drones can hug the terrain to hid from radar.
“There are multiplier effects to ‘layering’ different types of air defense units and ‘integrating’ them all with each other and to multiple sensors. It appears that the Armenians didn’t do this seriously.”  Loitering munitions can also stay low to the terrain or even masked behind terrain features such as hills and valleys. Bait aircraft are viable for anti-air to fire and reveal themselves and then be taken out from a suicide drone in hiding. 
In Yemen rebel, “Low-flying UAVs have also gone undetected…” by the Saudi led, US supplied coalition air defenses. [2 ] “…UAVs have been successfully deployed to target and disable coalition air defenses, inflicting notable reputational damage.” Succeeding where their missiles did not. The “unsophisticated UAV attacks are humiliating for a coalition led by the Middle East’s largest military spender.” 
Sadi Arabinan had help in air defense network. Top of the line US equipment and ???Advisers”””seems air defense could counter super local drone attacks because where built for planes and stragertigc point defense in mind- lost source although
“The Ukrainian experience demonstrates that UAV defense and traditional air defense should be integrated. A wide variety of drones have been deployed in support of the 1st and 2nd Army Corps deployed in eastern Ukraine, and the Ukranian air defenses have shot down some 45% of drones in the conflict, with another 40% downed by small arms fire and the final 10% with electronic measures.”